Patent Publication Number: US-6669246-B2

Title: Lock

Description:
CROSS REFERENCE TO RELATED APPLICATION 
     This application is a 35 U.S.C. §371 of POT International Application Number PCT/GB01/00741, which was filed Feb. 22, 2001 (22.02.01), and was published in English. 
    
    
     This invention relates to a lock for a movable wing, and particularly to a lock intended to be rim fitted to a domestic entrance door. 
     According to the invention a lock for a wing movable between respective open and closed positions relative to a frame comprises a casing, a bolt operable to extend from the casing or to retract into said casing to a first, normally retracted position, and bolt retention means manually operable at one side of the wing, in use, the bolt retention means being inoperable when said bolt is in its said first, normally retracted position, the bolt being movable in a direction into the casing from its first, normally retracted position, to a second retracted position in which said bolt retention means is operable to a position to retain the bolt retracted. 
     Preferably said bolt retention means retain the bolt in its first retracted position. More preferably said bolt is releasable from its retention in its first retracted position only by movement of the bolt to its said second retracted position. Desirably said release of the bolt from the bolt retention means is automatic when said retained bolt reaches its second retracted position. Conveniently in said second retracted position, part of said bolt engages a rear wall of the casing. 
    
    
     The invention will now be described, by way of example, with reference to the accompanying drawings, in which: 
     FIG. 1 is a schematic internal side view of a casing of a lock of the invention, with a bolt thereof in its normally retracted state and a handle in its rest position, 
     FIGS. 2 and 3 are respective views similar to FIG. 1, showing the bolt partly and fully extended from the lock casing, 
     FIG. 4 is a view corresponding to FIG. 3, but with the handle partly pivoted from its rest position, 
     FIG. 5 is a view corresponding to FIG. 4, with the handle fully pivoted and the bolt in its normally retracted state, 
     FIG. 6 is a schematic fragmentary, internal plan view of the lock casing, with the bolt in its fully extended, deadlocked state, 
     FIG. 7 is a schematic fragmentary, internal view at 90° to FIG. 6, 
     FIGS. 8 and 9 are views corresponding to FIGS. 6 and 7 respectively, but with the bolt in its normally retracted state, 
     FIG. 10 is a view corresponding to FIGS. 6 and 8 showing a cam member in two alternative positions at the commencement and end of bolt retraction respectively by said cam member, 
     FIGS. 11 and 12 are views corresponding respectively to the two views of FIG. 10, 
     FIG. 13 is a simplified schematic internal side view of the lock casing showing a snib for locking the bolt in its retracted position, the bolt being shown in its normally retracted state prior to actuation of said snib, 
     FIG. 14 is a view corresponding to FIG. 13, but with the bolt retracted further into the casing and the snib actuated, 
     FIG. 15 is a view corresponding to FIGS. 13 and 14, with the bolt in its normally retracted state and the snib actuated to lock the bolt, 
     FIG. 16 is a fragmentary, schematic internal simplified, side view of the casing showing a spring loaded catch and associated bolt retention element, 
     FIG. 17 is a fragmentary plan view corresponding to FIG. 16, with the bolt retention element retaining the bolt in its normally retracted state, 
     FIG. 18 is a view corresponding to FIG. 17, but with the catch depressed to release the bolt retention element to allow the bolt to move to its extended position, 
     FIG. 19A is a schematic, fragmentary side sectional view of the casing showing a key operated lock cylinder arranged at one side of the lock casing having been operated to cause movement of blocking means to a position to prevent operation of the handle to retract the bolt, 
     FIG. 19B is a schematic, fragmentary, split part-sectional view showing how a rose around said lock cylinder of FIG. 19B is secured to said one side of the casing, 
     FIG. 19C is a schematic, split part-sectional view of the lock casing as in FIG. 15, but showing the lock cylinder of FIG. 19C, 
     FIG. 20 is a diagrammatic plan view of the arrangement of FIG. 19A, 
     FIGS. 21 and 22 show positions of the lock cylinder plug relative to the blocking member when the blocking member is moved clear of the handle, before the key turns the plug to the key removal position and after the plug has been turned respectively, 
     FIG. 23 is a simplified internal plan view showing the fixing of the lock casing to one side and front edge surface of a door, 
     FIG. 24 is a schematic reduced scale view similar to FIG. 19, showing a housing which receives the lock cylinder in position to be fitted to the lock casing, 
     FIGS. 25 and 26 are schematic reduced scale views similar to FIGS. 3 and 2 respectively showing bearings for the bolt deadlock element and the handle, the handle not being shown in FIG. 26, 
     FIG. 27 is a scrap view of the housing in the direction of arrow A of FIG. 24, 
     FIGS. 28 and 29 are opposite side views respectively of the housing of FIG. 24, 
     FIG. 30 is an interior plan view of a main body part of the lock casing when empty, 
     FIG. 31 is a scrap side view of part of a locking assembly operable at the outside of the door, and 
     FIGS. 32 a  and  32   b  respectively show a bar of the locking assembly of FIG. 31 engaged with the blocking member of FIGS. 19 to  22  in two positions. 
    
    
     Shown in the Figures is a lock of the invention, which in the illustrated embodiment is rim mounted, i.e. as shown in FIG. 23, is intended to be mounted at one side and partly at one front edge surface of a wing such as a conventionally hinged door  10  which has an associated frame and staple (not shown) so that the door can be moved between an open position and a closed position in which it is locked by a bolt of the lock, such bolt being described hereinafter. 
     The lock has a metal casing made up of a main body part  11 , in the general form of a square box structure having one side open, and a closure part  12  in the form of a flat square metal plate. The plate has respective holes at or adjacent each of its four corners for fixing screws passing into respective threaded bores in bosses formed with the body part  11 , to secure part  12  in place inwards of the plane of the outer free edge surface of the part  11 , and to complete the lock casing with the assembled components therein concealed from view. 
     As mentioned, the main body part  11  is in the form of a square box-structure and FIG. 23 shows a side wall  13  integrally formed with an end wall  14  and a front wall  15  which is extended from the side wall  13  further than the end wall  14  to form a forend of the lock, with the extension part of the wall  15  being secured to a front edge surface of the door  10  as shown in FIG. 23, with the free edge surface of the end wall  14  engaging against the inner side of the door, in use, again as shown in FIG.  23 . The main body part  11  is completed by a bottom wall  16 , and a parallel top wall  17  shown in FIGS. 17 and 18. 
     The extended part of the front wall  15  is formed with a spaced pair of countersunk holes adjacent its upper and lower edges respectively, one of which  18 , is shown in FIG. 23, these countersunk holes receiving corresponding screws, such as screw  19  shown in FIG. 23, for securing this extension of the front wall  15  in a corresponding depth rebate in the front edge surface of the door  10 . In the front wall  15 , at a position just inward of the plane defined at the open side of part  11 , are a pair of spaced countersunk holes, one of which  20  is shown in FIG.  23 . At substantially the same level from the side wall  13  as the countersunk holes  20  is provided on the interior of the end wall  14  an integral lug  21  which has a circular-section hole  22  therethrough, the plate  12  having a cut-out to accommodate the lug  21 . The outer surface of the lug is spaced from the outer free edge surface of the body part  11  by the thickness of a flat mounting plate  12   a . This lug  21  is centrally disposed along the end wall  14 , and the plate  12   a  has a tapped hole  23  adjacent one of its edges centrally along the length thereof, so that, as shown in FIG. 23, with the plate  12   a  in place at the ‘open’ side of the main body part  11 , the plate  12   a  can rest on the outer surface of the lug  21 , at a position spaced from part  12 , so as to lie flush at said ‘open’ side of the body part  11 , with the hole  23  aligned with the hole  22  through the lug. Moreover, at its edge surface opposite to its edge surface adjacent which the hole  23  is provided, there are two integral bent down tags, one of which,  24 , is shown in FIG.  23 . Each tag extends through a slot in part  12 , and has a tapped hole therethrough this being shown as  25  for tag  24 . With the plate  12   a  arranged, as described, flush at the outer ‘open’ side of the body part  11 , the holes through the respective tags are aligned with the countersunk holes  20  to receive fixing screws, one of which,  26 , is shown in FIG.  23 . In use, as shown in FIG. 23, a screw  27 , captive in the hole  22  in the lug, has its shank engaged in the aligned tapped hole  23  in the plate  12   a , with its free end received in a recess in the side surface of the door. Accordingly in this way the completed casing, comprising the main body part  11  and part  12 , is secured to the mounting plate  12   a , and by way of the screws  19  the completed casing is also secured to part of the front edge surface of the door. The fixing of the plate  12   a  to part  11  is particularly convenient as compared to prior art arrangements where the equivalent component is often a complicated pressing with tags, slots and the like for securement to the lock case. The plate  12   a  has two countersunk fixing holes therein, one spaced above the other, for wood screws to fix it to the side of the door. One hole  12   b  is shown in FIG.  23 . The fixing of the screw  27  forms the subject of our UK Patent Application No. 0005755.4 from which our co-pending International Patent Application No. PCT/GB01/00731 (Publication No. WO 01/69017) claims priority. 
     Additionally as shown in FIG. 23, the plate  12   a  has a lock cylinder and plug assembly  28  secured thereto. The assembly is positioned on the plate  12   a  centrally over a circular hole (not shown) in the plate  12   a , with respective projections from the end of the cylinder at respective opposite sides of said hole in the plate  12   a , extending into correspondingly shaped openings respectively in the plate  12   a . To secure the assembly  28  in this located position on the plate  12   a , the plate has a pair of spaced aligned holes  29  therethrough at opposite sides of the hole in the plate  12   a  at which the assembly is centred, and screws  30  are respectively engaged in the holes  29 , with the shanks of said screws extending into respective threaded bores  31  in the cylinder of the assembly  28 . 
     In use, as shown in FIG. 23, the completed casing is secured to the door as shown, with the assembly  28  received in a circular-section opening through the door, the end of the assembly projecting from the other side of the door and having fixed therearound a rose  32  or equivalent member. The rose can have a pair of rearwardly directed bosses, arranged diametrically at the top and bottom of the assembly  28 , and received in respective bores in the door, and these bosses can be aligned with respective bolts, one of which is shown in FIG. 23 by the numeral  33 , which extend through respective holes in the plate  12   a , with the shanks of the bolts extending through the thickness of the door  10 . In one arrangement the threaded ends of these bolts can be engaged in open threaded ends respectively of the rearwardly extending bosses of the rose  32  so as tightly to secure the rose to the outer surface of the door as shown in FIG.  23 . With the arrangement described, therefore, and as shown in FIG. 23, the lock casing is securely secured to one side of the door with its lock cylinder and plug assembly  28  secured through the door and accessible for operation at the opposite side thereof. Schematically shown in FIG. 31 is a plug  28   a  and operating bar  28   b  of assembly  28 . 
     A central edge part of the side wall  13  is provided with a rectangular opening  34  schematically as identified in FIG. 23, and a communicating similar rectangular opening  35  is provided in the adjoining edge part of end wall  14 . At opposite ends of the opening  34  the interior surface of side wall  13  is provided with respective concave semi-cylindrical bearing surfaces for pivotally mounting a handle  36  which extends through the openings  34  and  35 , as will be described. The bearing surfaces  34   a  are identified in FIGS. 24,  26  and  30 . 
     Disposed centrally in the side wall  13  and spaced a little way inwardly of the inner edge of the opening  34 , is an oval hole  37  in which is fitted a housing  38  for a lock cylinder  39  and its associated plug  40  as shown in FIGS. 19 and 25. This housing  38  is in the form of a metal casting, e.g. of zinc based alloy, and also includes a pair of parallel spaced arms  38   a  which have respective concave semi-cylindrical bearing surfaces  38   b  defined therein as shown in FIGS. 24,  26  and  29 . The bearing surfaces  38   b  mate with the corresponding bearing surfaces  34   a  to form a pair of spaced full bearings for a pivot rod  41  which is located in a part circular channel  42  (FIGS. 19A,  21 ,  22  and  23 ) adjacent an inner edge of the handle  36  so as to allow pivoting of the handle  36  relative to the casing. Respective opposite end portions of the rod  41  pass through respective opposite ends of the handle which close the channel  42 , and extend outside of said handle ends into said full bearings respectively. Full pivoting of the handle, as shown in FIGS. 5 and 23, is required to allow access through a cut-out  36   a  in the end of the handle, and through openings  34 ,  35 , for a screwdriver shank  27   a , to enable it to engage the screw  27  both on assembly of the lock casing to the door, or for removal. 
     The housing  38  also provides, adjacent said spaced arms thereof, respective fixing holes  38   c  therethrough, these holes being aligned with respective internally threaded bosses  13   a  upstanding from the inner surface of the side wall  13 . By the use of fixing screws, the housing  38  is thereby secured to said side wall of the casing. This side wall has two holes  13   c ,  13   d  therethrough at respective opposite sides of the part of the housing which extends outwardly from said side wall  13 , these holes being on a diameter through the centre of the lock cylinder  39  and its associated plug  40 . The part of the housing  38  within the casing is provided with one hole  38   d  aligned with the hole  13   c  in the side wall  13  and also a cut-away  38   e  which is aligned with said other  13   d  of said diametrically aligned holes in the side wall  13 . The shanks of respective headed fixing screws  38   h  (FIGS. 19B and 19C) are received through said holes  13   c ,  13   d  in the side wall  13 , with the heads received in said hole  38   d  and cut-away  38   e  respectively. The respective threaded ends of these fixing screws are threadedly received in blind bores in the inner surface of a rose  110  which is fitted around the part of the housing  38  projecting outwardly of the casing, this rose being pulled by said fixing screws against the outer surface of the side wall  13  so as to conceal from view, and to prevent access to, a grub screw hole  38   f  with associated grub screw  38   g , extending through the housing  38  at the exterior of the casing, this grub screw engaging in a recess in the outer side of the cylinder  39 , thereby to secure the cylinder, with its associated rotatable plug therein, to the housing  38 . The respective post-drive heads of these fixing screws extending through the casing part  11  to secure the rose in place are arranged to be uncovered and easily accessible within the casing part  11  when the assembly of casing part  11  and closure part  12  is removed from the plate  12   a  on the door in use, and with the bolt of the lock held retracted, without having to remove components of the lock from the casing part  11 , thereby making cylinder removal and replacement much easier than with known arrangements. The plate  12  has holes  12   c  therein aligned with these fixing screws respectively. Once the casing part  11  is removed from the door, all that is required is an undoing of said uncovered fixing screws, the heads of which move into previously ‘empty’ parts of hole  38   d  and cut-away  38   e , to release the rose  110 , thereby uncovering the grub screw  38   g . This is then undone, allowing the cylinder  39  and plug  40  to be changed at the outside of the casing part  11 . The grub screw is then retightened, the rose replaced and the fixing screws tightened to secure the rose to the surface of side wall  13 . This feature forms the subject of our UK Patent Application No. 0005753.9 from which our co-pending International Patent Application No. PCT/GB01/00722 (Publication No. WO 01/69016) claims priority. On assembly the rose  110  can firstly be secured in place by screws  38   h  and the housing  38  secured in place thereafter. 
     The structure of the housing  38  within the casing, provides four further functions. Firstly, it has two further spaced arms  138   a  defining respective concave semi-cylindrical bearing surfaces  138   b , the arms and the bearing surfaces being shown in FIGS. 24 to  29 . The arms  138   b  extend away from the end wall  14  and the surfaces  138   b  are directed towards the interior surface of the side wall  13  where said bearing surfaces  138   b  mate with corresponding respective concave semi-cylindrical bearing surfaces  13   b  formed on projections upstanding from the interior surface of the side wall  13 . This pair of completed spaced bearings act as a pivoting arrangement for a rod  43  of a deadlock element  44  shown best in FIGS. 1 to  5 , FIGS. 7 to  12 , and FIGS. 25 and 26. 
     As shown in these Figures, the deadlock element has a rectangular body part  45  extending away from the rod  43 , the part  45  having a downturned nose  46  at its end remote from the rod. At the longer side of the body part  45  facing the top wall  17 , the body part has a U-shaped projection  47  which is open upwardly and outwardly. The lower interior surface of the projection  47  is substantially at the level of the underside of the body part  45 , but at the location of this projection  47 , the side of the body part has its lower portion recessed, as shown at  48 , so as to receive, as will be described, a straight end part of a spring-like connecting member  49  which links the handle  36  to said deadlock element  44 . A second function provided by the housing  38  is a provision of a pair of upstanding surfaces  138   c  which define between them a guide slot  138   d  for a further part  50  of the spring-like connecting member  49  which extends to co-act with the handle  36 . As shown in FIGS. 1 to  5 , the handle, at its side adjacent the top wall  17  has an arm  51  extending from said channel  42 , this arm defining a nose part  52 . At its inner side, spaced slightly downwardly from the top of the nose part  52 , as viewed with the orientation of the nose part shown in FIGS. 1 to  3 , is a further, smaller nose part  53 , the parts  52  and  53  being spaced by a section defining a groove  54 . This groove is to receive said further part  50  of the spring-like connecting member  49 , as shown in FIGS. 1 to  5 , whilst the further nose part  53  is to engage an end of a bolt  55  of the lock, as will be described hereinafter. 
     As shown in FIGS. 1 to  5 , the connecting member  49 , which is of spring steel, has a central coiled part  56 , which is received on the rod  43  which acts as the pivot for the deadlock element  44 . At the end of the coiled part  56  remote from the top wall  17 , the member is formed with a straight part  57 , lying in a plane parallel to the walls  16  and  17 , this having its end turned through 90° to provide the previously mentioned straight part which extends into the recessed portion  48  of the body part  45  of the deadlock element  44  as shown in FIGS. 1 to  5 . At the other end of the coiled part  56 , the further part  50  extends away from the side wall  13 , through the guide slot  138   d , and into the interior of the casing where it is formed with a concave kink  58  and then a convex kink  59  before terminating in a slightly arcuate end portion  60 . This further part  50  of the connecting member  49  lies in a plane parallel to the top wall  17  which is in the same plane as the groove  54 . As will be explained further for the lock, in use, it can be seen from FIGS. 1 and 2 that with the bolt in its fully retracted or partly extended position the kink  58  and kink  59  are spaced clear of said groove  54 . However, in the filly extended position of the bolt  55  shown in FIG. 3, as the deadlock element  44  pivots into the interior of the casing, the kink  58  moves into said groove. If from this position the handle  36  is now pivoted to retract the bolt  55 , it can be seen that this part of the connecting member  49  is lifted at the kink  59 , such that the straight part  57  of member  49  acts to move deadlock element  44  pivotally back to its FIG. 1 position. Accordingly the bolt is no longer prevented from moving inwardly by element  44  and is retracted as the handle is pivoted to its FIG. 5 position. 
     FIG. 5 shows the position reached when the handle is in its fully pivoted position relative to the casing so that its nose part  52  engages the end wall  14 , with the end portion  60  of the connecting member  49  being raised in the groove  54  to its innermost position in the casing where it lies adjacent the inner surface of the closure part  12 . From these Figures it will be noted that from the inner side of the body part  45  there is a cylindrical projection  61  with a hemi-spherical head, whilst on the same axis, but at the opposite side there extends an identical but smaller diameter projection  62 . This projection  62  is movable through a slot  63  in the side wall  13 , and the inner surface of the side wall  13  is formed with a circular section pocket  64  around the slot  63 , with a coiled compression spring  65  being received around the projection  62  and having its one end located in said pocket. In this way, the deadlock element  44  is biased to pivot inwardly into the casing, to the position shown in FIG. 3, with the projection  62  acting as an indicator at the exterior of the side wall  13  of the lock to indicate whether or not the bolt  55  is deadlocked. As explained, pivoting of the handle from its FIG. 3 to its FIG. 5 position causes, by way of the intermediary of the connecting member  49  overcoming the force of spring  65 , pivoting of the deadlock element  44  to its FIG. 1 position, and accordingly, as will be explained, retraction of the bolt  55 . The feature of the connecting member forms the subject of our UK Patent Application No. 0005756.2 from which our co-pending International Patent Application No. PCT/GB01/00746 (Publication No. WO 01/69018) claims priority. 
     The housing  38  further provides a pair of spaced inwardly directed arms  66  (FIGS. 16 to  18  and  28 ) and upstanding from the inner surface of the side wall  13  are a pair of spaced parallel guide walls  67  extending normal to the top and bottom walls  16 ,  17 , these guide walls  67  lying slightly inwards of the inner surface of the front wall  15 , as shown schematically in FIG.  16 . Each guide wall is interrupted by a generally rectangular slot  67   a  extending inwards from the outer free edge surface of the guide wall, the two slots being aligned with each other, and also with the opening defined between the two arms  66 . Moreover, the front wall of the casing is formed with a rectangular slot  68  which is in the same plane as, and thus aligned with, the aligned slots of the guide walls  67  and the opening between the arms  66 . This arrangement is to accommodate a spring loaded bolt release member  69  shown in FIGS. 16 to  18 . The member  69  is of elongate form having a tail part  70 , which is straight with an upturned end, a coiled compression spring  71  being disposed around the straight section of part  70 . The part  70  is arranged to engage in the opening between the arms  66 , with one end of the coiled compression spring engaging against the respective sides of the arms facing the front wall  15 . The other end of the spring abuts a main body part  72  of the member  69 , this being arranged to slide across the guide walls  67  by being received in the slots which interrupt said guide walls as described. At the free end of the body part  72  is a chamfered nose part  73  which is arranged slidingly to extend through the slot  68  as a close sliding fit, as best shown in FIGS. 16 and 18 which represent the fully extended and fully retracted positions respectively of the member  69 . Lying between the guide walls  67  on a part cylindrical bearing surface defined between said guide walls  67 , is a cylindrical bolt holding member  74  which is arranged automatically to engage with die bolt  55  in its normally fully retracted positions shown in FIGS. 1 and 5. The member  74  is biased by a coil spring  75  received between the top wall  17  and an end of the member  74  to move it away from the wall  17 . Along its length, the member  74  is provided with a transverse recess  76  in which is received the main body part  72  of the bolt release member  69 . This main body part  72  is of two thicknesses joined by a chamfered surface  77  which, in this embodiment, faces the top wall  17  as shown in FIGS. 17 and 18. The position of this chamfered surface  77  along the length of the bolt release member  69  is such that when the member  69  is in its fully extended position shown in FIG. 16, the thinner portion of the main body part  72  is within the recess  76 , adjacent the side of the recess nearest the top wall  17 . However, as the member  69  is extended into the casing, the chamfered surface  77  engages the edge of the recess  76  nearest the top wall  17 , so that as the linear inwards movement of the bolt release member  69  continues, this chamfered surface forces the member  74  in a direction towards the top wall  17  against the bias of its spring  75 . At its opposite end to that at which the spring  75  abuts, the member  74  has a pin  78  adapted to engage in a recess  79  defined in one longitudinal side of the bolt  55 . 
     Accordingly it can now be appreciated from FIGS. 17 and 18 how this pin  78  of the member  74  is spring biases to engage in said recess  79 , and thus to hold the bolt in its normally retracted state with the bolt release member  69  spring loaded to its fully extended position. However, as will be described, when the door  10  is closed, the member  69  is automatically forced into the casing against its spring bias, by engagement with the staple at the doorframe, so that, as the member  69  moves to its FIG. 18 position, its chamfered surface  77  moves the member  74  against its spring bias to release the pin  78  from the recess  79  of the bolt  55  which then automatically moves to its extended position under the bias of a coiled compression spring (not shown) which is received in a longitudinal guide  213  which is parallel to and spaced inwardly of the bottom wall  16 , this guide extending upwardly from the side wall  13  and extending to the inner surface of the front wall  15 . The bolt  55  is provided with a peg extending from its side facing the side wall  13 , this peg extending into the guide and thus serving to compress the spring therein when the bolt is moved to its normally fully retracted position and held by member  74 , release of the member  74  normally thus allowing this spring to extend in its guide, thereby moving the peg along said guide and causing extension of the bolt. 
     A final function provided by the housing  38  is that, in one embodiment, it is extended inwardly of its portion receiving the lock cylinder  39  and associated plug  40  to house a cylindrical component  80  having a radial blocking lug  81  extending from the outer surface thereof. If the housing  38  provides this function, then it receives part of the length of the component  80  within a cylindrical housing part which is provided with an arcuate cut-away portion therein which extends around approximately 100° of arc to allow for movement of the blocking lug  81  between its two extreme positions at opposite ends of said cut-away portion, whilst projecting outwardly from this portion of the housing  38  in which the component can rotate. For clarity, this inwardly extended part of the housing  38  is not shown in FIG. 19, but is shown in FIG. 28, the cut-away being indicated at  181 . 
     The component  80  has the lug  81  extending from its outer surface adjacent one end thereof, this end being the one which is adjacent the inner end of the plug  40  as shown in FIG.  19 . The end surface of the plug is recessed inwardly of the end surface of the cylinder, but with a projection  82  extending beyond the end of said cylinder. The end of the component  80  is formed with a reduced diameter part  83  which is sized to fit within the recess defined at the end of the cylinder, so that this end part  83  is received in engagement with the end of the plug. However this end part  83  of component  80  does itself have a recess  84  therein extending over approximately 60° of arc, with the projection  82  being received in said recess, so that when the plug is rotated by operation of a key in the plug  40  at the inside of the door this projection  82  will rotate the component  80  under some circumstances where the projection is in engagement with one of the side surfaces of the recess  84 , as will be described. The provision of the recess  84  does however provide for lost motion between the plug and the component  80  so that the plug can be brought back to its position in which the key can be removed from the lock cylinder, whilst leaving the component  80  in its rotated position. 
     The opposite end of the component  80  has a generally central circular-section bore therein, but within said bore are a pair of diametrically opposed projections  80   a  (FIGS. 32A and 32B) of V-shape, with the respective apices of the two shaped projections being spaced apart but facing one another. The side faces of each projection are flat, and arranged so that the operating bar  28   b  of the plug  28   a  of the assembly  28  is received in this bore in such a manner that key operation of the assembly  28  from the exterior of the door will cause the bar to engage one side of one of the projections on one of its sides and one side of the other projection at its other side so as to turn this component between its opposite extreme positions (FIG.  32 B). The annular form and spacing of the projections means that, again, there is lost motion between the locking bar, i.e. the cylinder and plug assembly  28  and the component  80 , it being appreciated that in one direction of rotation the bar will engage one flat surface of one projection and one flat surface of the other projection, whilst in the other direction of rotation the bar will engage respective opposite surfaces of said projections to turn the component  80  in the other direction, again the lost motion allowing the plug and cylinder assembly  28  to be moved to a position (FIG. 32A) relative to the component  80  where the key can be removed. FIGS. 20 to  22  and FIG. 28 show schematically two small angularly spaced apart semicircular section recesses  85 ,  86  in the interior surface of the extended part of the housing  38  in which part of the component  80  is received, and each recess selectively mates with a small bore  87  in the exterior surface of the component  80  angularly spaced therearound from the lug  81 . A small spring is received in said bore  87  and at the end of this is a small ball. In this way the ball is spring biased across the interface between the component  80  and each recess  85 ,  86  as relative rotation takes place between the component  80  and the housing  38 . In other words in each of its extreme positions, the component  80  is held substantially firmly in place, against inadvertent rotation, by the spring loaded ball. 
     FIG. 20 shows that the handle is provided, adjacent its channel  42  with a centrally disposed projection  88  which has a flat surface which faces the closure part  12  when the handle is in its rest position shown in FIG.  19 . At its one side, this projection is provided with an upstanding wall  89  which acts as a stop. The position of this projection relative to the component  80  is such that under normal conditions the blocking lug  81  is in the position shown in FIG. 21 or FIG. 22 where it is clear of the projection  88  so that the handle can be pivoted as previously described in relation to FIGS. 4 and 5 to retract the bolt  55 . If, however, as briefly described above, the component  80  is moved angularly from its extreme position shown in FIGS. 21 and 22 to its other extreme position shown in FIG. 20, the blocking lug  81  will lie over the flat surface of the projection  88 , if the handle is in its rest position, the lug  81  engaging against the stop wall  89  as shown in FIG.  20 . In this position pivoting of the handle is prevented by the blocking lug  81 . In relation to the handle  36 , it is to be noted that a coiled torsion spring (not shown) is received around the pivot rod  41 , with one end of the spring engaging against the end wall  14  and the other end engaging against the channel  42  so as to bias the handle to its rest position shown in FIG.  19 . 
     As shown in FIGS. 13 to  15 , and also in FIGS. 1 to  5 , the bolt  55  is of generally laminar construction being made up generally of a series of interconnected plates all defining a generally rectangular leading end part which extends into and out of the casing through a correspondingly shaped opening  91  in the front wall  15  of the casing. Defined through the centre of the bolt at a position inwards of said leading end part is a slot  92  in which is received the cylindrical projection  61  as shown in FIGS. 1 to  5 . Whilst the two innermost and also the two outermost plates  90  defined relative to the side wall  13  terminate at the end of or shortly beyond the end of the leading end part of the bolt, the middle plate, denoted by the numeral  93 , is of greater extent from said leading end part and defines two arm portions  94 ,  95  at opposite sides of the slot  92  which is extended to the end of the plate  93  remote from said leading end part. At the free end of the arm portion  94 , part of the plate  93  is turned through 90° to form a foot  96  which is directed towards the plate  12 . Similarly the free end of the arm portion  95  is also turned through 90° to provide a foot  97  again directed towards the plate  12 . As will be appreciated from FIGS. 1 to  5  and  13  to  15 , the foot  97  is for engagement by the further nose part  53  to retract the bolt from its extended position, whilst the foot  97  is for engagement by a driving surface  98  of a cam  99  to be described with reference to FIGS. 6 to  12 . 
     FIG. 3 shows that with the bolt fully extended and the handle in its rest position, the further nose part  53  is spaced from the foot  97  of the bolt. This is to allow for the movement of the further part  50  of the connecting member  49  to its FIG. 4 position by the pivoting of the handle, thereby moving the deadlock element  44  clear of the bolt, before the further nose part  53  engages foot  97  to retract the bolt. In this way, retraction of the bolt is unhindered by the element  44 . Similarly FIG. 6 shows that the surface  98  of the cam is spaced from the bolt foot  96  when the bolt is fully extended and the cam is in its rest position. This allows initial cam angular movement by a key, as will be described, to move the element  44  clear of the bolt (FIG. 11) before the surface  98  engages the foot  96  to retract the bolt. Thus again retraction of the bolt is unhindered by the element  44 . 
     The arm portion  94  has a hole  100  therethrough adjacent the foot  96 , this hole  100  aligning, in a retracted position of the bolt, with one of the holes  12   c  and the holes  13   b  and  38   d  to provide access for a screwdriver shaft to one of the fixing screws  38   h . In an outer edge of the other arm portion  95  is formed a circular section recess  101  which again, when the bolt is in said retracted position, aligns with the other of the holes  12   c  and the hole  13   c  and cut-away  38   e , to allow screwdriver access to the other of the fixing screws  38   h . In this manner with the bolt in a retracted position, and, as previously described, the assembly of lock casing part  11  and plate  12  removed from the door, the respective heads of both of these screws  38   h  holding the rose  110  are then accessible to allow the screws to be undone, in order to allow for removal of the rose, and easy replacement of the lock cylinder  39  and associated plug  40 , this aspect of the invention, as mentioned, forming the subject of our UK Patent Application No. 0005753.9 and corresponding International Application No. PCT/GB01/00722 (Publication No. WO 01/69016). It can be arranged that the retracted position of the bolt for access to screws  38   h  is the one when it is held by the member  74  in FIG.  17 . 
     In an outer edge of the arm portion  94  there is provided a cut-out  102  to allow for assembly of the spring which biases the bolt outwardly, into its guide  213 . Finally a circular hole  103  is provided in the arm portion  94  adjacent its end thereof nearest the leading end part of the bolt, but clear of the other four plates  90  of the bolt. In conjunction with this hole  103 , there is provided in the side wall  13  a circular section through opening  104  which at the inside surface of the side wall is provided through a boss  105 . Extending through said opening  104  and into said boss is a snib  106  for retaining the bolt in its normal fully retracted position as shown in FIGS. 13 to  15 . The snib  106  has a head  107  which is visible from the exterior of the side wall  13  and which allows the snib to be manually operable from inside of the door to which the lock is fitted, in use. From the head  107 , the snib is stepped downwardly twice to define a central reduced diameter part  108  and an end further reduced diameter part  109 , all the parts being about a common central axis. A circlip  110  is engaged in a groove of the snib at the junction between the parts  108  and  109 , and a coil spring  111  is received around the central part  108 , with its one end engaged against an underside of the head  107 . The snib is fitted at the opening  104  and boss  105  as shown in FIGS. 13 to  15 , so that the other end of the spring is engaged against a step at the inner part of the boss so that the snib is normally biased outwardly to its FIG. 13 position where the circlip  110  acts as a stop against the innermost surface of the boss to hold the snib in place at the casing. 
     Although the hole  103  is of a size to receive the part  109  of the snib therein, it can be seen from FIG. 13 that in its normal fully retracted state, i.e. with the nose part  52  of the handle  36  in engagement with the end wall  14 , this hole  103  is out of alignment with the part  109  of the snib. However it will also be noticed that the foot  97  has itself not yet reached the inner surface of the end wall  14 . Accordingly in order to operate the snib, it is first necessary to push the bolt rearwardly from its FIG. 13 position by applying pressure to its leading end part. This moves the foot  97  into engagement with the inner surface of the end wall  14  as shown in FIG. 14, thereby aligning the hole  103  with the part  109  of the snib, allowing the snib to be moved into said hole against its spring bias. Once the part  109  of the snib has been moved into the hole  103 , the inwards pressure on the end of the bolt can then be released, and the spring acting on the bolt will move it back to its normal fully retracted position shown in FIG. 15, with the part  109  of the snib retained in the hole  103 , which, it will be appreciated, is somewhat oversized in relation to the diameter of the part  109  so as to allow for said movement of the bolt between its FIGS. 14 and 15 positions respectively. It can be seen that, if required, the free end of the part  109  can be provided with a narrow flange to define, with the circlip  110 , a neck held in hole  103 . Once the snib has engaged the bolt as shown in FIG. 15, release of the snib can only be effected by again applying inwards pressure to the end of the bolt, thereby releasing engagement of the bolt at the edge of the hole  103  on the part  109 . The spring  111  then automatically moves the released snib back to its FIG.  13  position and the greater projection of the head  107  at the outside of the side wall  13  indicates that the snib is no longer engaged, so that in closing the door, the bolt will automatically extend as described herein above. Although as described and shown, the snib holds the bolt in its FIG. 17 retracted position, the snib could alternatively be arranged to hold the bolt in a position between the positions of the bolt in FIGS. 13 and 15 respectively. Accordingly the hole  100  and recess  101  would be re-positioned to allow access to screws  38   h , although with posi-drive screw heads a screwdriver shank at an angle thereto might still be able to undo the screws. The feature of the snib to lock the retracted bolt against release on closing the door forms the subject of the present application. 
     Finally with regard to the components of the lock, reference is made to FIGS. 6 to  12  which show the cam  99 , the driving surface  98  of which, as mentioned previously, acts, in operation, on the foot  96  to retract the bolt  55 . As will be described, the handle operates, in use, from the inside of the door to retract the bolt by way of the further nose part  53  acting on the foot  97 , whereas from the outside of the door key operation at the cylinder and plug assembly  28  moves this cam  99  and thus retracts the bolt by way of the driving surface  98  engaging the foot  96 . In its rest position, shown in FIGS. 6,  8  and  9 , a side surface thereof engages a stop  99   a  in the form of a lug or equivalent projecting inwardly from closure part  12  to prevent anticlockwise movement of the cam (as viewed in FIG. 6) from its rest position. 
     The cam  99  is provided on its one side with a hollow boss  112  (FIG. 19A) which is rotatably received on the end of the component  80  which has therein the bore containing said V-shaped projections. At the other side of the cam is an upstanding boss  113  which has the same centre as the boss  112 . A slot  114  for a locking bar of the cylinder and plug assembly  28  extends through the boss  113  and into the interior of the hollow boss  112 , rotation of the locking bar being effected upon key rotation of the plug of the lock cylinder and plug assembly  28  to rotate the component  80  as described, with there being lost motion between the cam  99  and the component  80 . As shown in FIGS. 6 to  12 , the surface of the cam at the side at which the boss  112  is provided is formed from an edge surface  115  disposed at approximately 90° around the cam from the surface  98 , with a first flat surface  116  and a second longer flat surface  117 , these two flat surfaces being joined by a ramp section  118 . FIGS. 6 and 7 show the arrangement where the bolt  55  is fully extended and deadlocked in this position by the nose  46  engaging the inner end of the plate  90  immediately adjacent the middle plate  93  at the side thereof facing the side wall  13 . As shown in FIGS. 1 to  5  and  13  to  15 , this plate which is in engagement with the middle plate  93 , extends further inward than the outer plate of this side of the bolt which faces the side wall  13  so that, as shown in FIG. 2, the nose  46  will also deadlock the bolt in its partly extended position, the nose then engaging the inner end of said outermost plate at this side of the bolt. 
     Accordingly as shown in FIG. 7, corresponding to the arrangement of FIG. 3, the bolt is held in its fully extended position with the hemispherical head of the projection  61  being in juxtaposition with the flat surface  116 . If key operation of the lock is now effected from the exterior of the door, the cam  99  will rotate as described and retract the bolt. FIG. 8 shows the position where the bolt is fully retracted and held in this position by the member  74 , the cam being returned by key rotation to its position shown in FIG. 8, FIG. 9 showing how the hemispherical head of the projection  61  is now spaced clear of the flat surface  116  as the deadlock element is now in its FIG. 1 position. FIG. 11 shows how the projection  61  is depressed as the can rotates, with the head of the projection  61  being forced against its spring bias as its head engages the ramp section  118 , this movement against its spring releasing the deadlocking of the bolt which can then be retracted by virtue of the driving surface  98  of the cam  99  engaging the arm portion  96  of the bolt. FIG. 12 shows the relative positions of the cam and the deadlock element in the position where the cam engages the arm portion  96  before the cam is moved by key rotation to return to its FIG. 8 position. With the bolt held fully retracted, key rotation will return the cam from its dashed FIG. 10 position of engagement with foot  98  back to its FIG. 1 position, where the cam engages its stop  99   a.    
     Operation of the lock, in use, will now be described. 
     With the lock fitted to the door  10  as shown in FIG. 23, the lock cylinder and plug assembly  28  is operable by a key from the outside of the door, the lock cylinder  39  and associated plug  40  of FIG. 19 being operable from the inside of the door by use of the same key. Conveniently each plug and cylinder assembly, and the key, may be of the form described and claimed in our pending published European Patent Application No. 0892130. 
     Normally, with the door  10  closed, i.e. received in its associated frame, the bolt  55  is in its fully extended position, for example as shown in FIG. 3, the leading end part of the bolt projecting from the front wall  15  being received in an associated keeper of any conventional form secured at or to the frame. In this state, the deadlock element  44  is in the position shown in FIG. 3 where it deadlocks the bolt  55 , as described, by acting as an abutment with the plate  90  of the bolt attached to the outer side of the plate  93 . In this deadlocked state, the projection  62  is fully received in the case, and this provides a visual indication at the inside of the door that the deadlocking is in operation. Moreover in this state, the handle  36  is in its rest position as shown in FIG. 3, the cam  99  is in its rest position as shown in FIG. 6, the snib  106  is in its rest position shown in FIG. 13, and the bolt release member  69  is in its retracted position shown in FIG. 18, being held against its spring bias by the engagement of the nose part  73  with the surface of the staple. As can be seen from FIG. 18, with the bolt release member in this position, the bolt holding member  74  is held by it clear of the adjacent side surface of the bolt. 
     In this deadlocked state, the door can be opened from the exterior by the use of the key for the lock in the assembly  28 . If the key is inserted into the plug of the assembly  28  and turned clockwise, as viewed in FIG. 20, the locking bar of the assembly  28  received in the slot  114  in the cam  99  will cause the cam to move angularly in a clockwise direction as viewed in FIGS. 6 to  10 . Firstly the driving surface  98  of the cam will move towards the foot  96 , and at the same time the ramp section  118  of the cam will engage the head of the projection  61  so as to begin moving it to release the deadlocking on the bolt, so that when the surface  98  engages the foot  96 , it can begin to retract the bolt into the casing as the projection  61  has now been engaged by the second longer flat surface  117  of the cam, as shown in FIG. 11, with the deadlock element  44  now being clear of the outer plate  90  of the bolt, as shown in FIG.  11 . The cam is then moved angularly by the locking bar until the bolt is in its normally fully retracted state, shown in dashed in FIG. 10, and as shown in FIG. 12 with the cam moved angularly to its extreme position. 
     In this state, however, unless the door is now opened, the bolt is not held retracted, given that the bolt release member  69  is still in its FIG. 18 position, preventing the bolt holding member  74  engaging the retracted bolt. Accordingly once the bolt is fully retracted, it is necessary to open the door, whereupon the bolt release member  69  is released from its engagement with the frame and, under its spring bias, slides to its FIG. 17 position where its nose part  73  extends from the front face of the lock. This sliding allows the bolt holding member  74  to move under its spring bias, to its FIG. 17 position where its pin  78  engages in the recess  79  in the side of the bolt, thereby holding the bolt in its retracted state. The key, and thus the plug of the assembly  28  can now be returned to its rest/key insertion position and the key removed. This return movement of the key brings the cam  99  from its one extreme position, shown in FIG.  12  and in dashed in FIG. 10, to its other extreme or rest position shown in FIG. 8, with the bolt retracted, the deadlock element  44  being in the position shown in FIG. 1 merely in engagement with one side of the bolt, with its projection  62  projecting from the exterior surface of side wall  13  to indicate that the bolt is not deadlocked. 
     Once at the inside of the door, a user can then close the door, which action automatically ‘throws’ the bolt, thereby locking the door. This is accomplished merely by closing the door from the inside, since this will cause engagement of the nose part  73  of the bolt release member  69  with the staple, thereby forcing this member  69  into the lock casing from its FIG. 17 position to its FIG. 18 position, this resulting in withdrawal of the bolt holding member  74 . As a consequence the bolt is automatically extended under the force of its biasing spring so that it is shot out of the casing to its FIG. 3 position, with the deadlock element  44  operating automatically as shown in FIGS. 1 to  3  again to deadlock the bolt. 
     Thereafter to open the door from the inside, it is merely necessary to pivot the lever  36  at the inside of the door from its rest position shown in FIGS. 1 to  3  to its fully pivoted position shown in FIG.  5 . This pivoting of the lever is transmitted via the connecting member  49  to the deadlock element  44  so as to move this firstly to its FIG. 4 position, where it no longer deadlocks the bolt, and then to its FIG. 5 position where the bolt is fully retracted into the casing by virtue of the further nose part  53  of the handle engaging the foot  97  of plate  93  of the bolt as shown in FIGS. 4 and 5, this retraction of the bolt taking place against its biasing spring, with pivoting of the handle also taking place against its own biasing spring. Once the FIG. 5 position is reached, it is again necessary to open the door in order to retain the bolt in its retracted position by means of the bolt holding member  74 . Accordingly, as previously described in order to hold the bolt retracted when entering from outside, opening of the door from the inside by way of the handle will again cause the bolt release member  69  to extend out of the casing, thereby releasing the bolt holding member  74  which moves under its spring bias to engage in the recess  79  in the bolt to hold it retracted. Thereafter closing the door causes the nose part  73  of the bolt release member  69  to engage the frame and be pushed inwardly, so as to move the bolt holding member  74  from its engagement with the bolt, which is thus then automatically extended out of the casing under its biasing force, so that the closed door is again automatically locked by the bolt entering into its associated keeper, the movement of the bolt from its extended to its retracted position, as shown in FIGS. 1 to  3 , also allowing the deadlock element to move as shown in sequence through FIGS. 1 to  3  so as again to deadlock the extended bolt in its keeper, thereby locking the door. It will be noted from FIG. 2 that due to the different lengths of the two bolt plates  90  at the side of the plate  93  facing the side wall  13 , the bolt is deadlocked not only in its fully extended position shown in FIG. 3, but also in its partly extended position shown in FIG. 2 where the nose  46  of the deadlock element  44  engages the shorter outermost plate  93  of said two plates at said one side of the middle plate  93 . This feature ensures a secondary locking position to provide security should the bolt not fully extend for any reason. 
     A feature of the lock relates to the locking of the handle  36  so that it cannot be operated from the inside of the door without the key for the lock, thereby preventing an intruder exiting through the door. This forms the subject of our UK Patent Application No. 0005752.1 from which our co-pending International Patent Application No. PCT/GB01/00735 (Publication No. WO 01/69015) claims priority. This feature is of particular benefit when the lock is used on glass panel doors. 
     To lock the door from the inside, the handle is firstly pivoted and the door opened, to hold the bolt in its retracted position. The key is then inserted into the plug  40  in its lock cylinder  39  in the housing  38 . In this key insertion state, the projection  82  of the plug is against one surface of the recess  84  of the cylindrical component  80  as shown in FIG. 22, with the lug  81  of component  80  clear of the projection  88  of the handle, so that in this state the handle can still be pivoted. If the key is now turned in an anti-clockwise direction, as viewed in FIG. 22, the plug turns, and thus the projection  82  of the plug acts on the component  80  to turn it also in an anti-clockwise direction to bring the lug  81  over the projection  88  and into engagement with the wall  89 , as shown in FIG.  20 . During this angular movement of the component  80 , the spring loaded ball associated with the component  80  moves from partial reception in the recess  86  to partial reception in the recess  85  thereby holding the component  80  in its FIG. 20 position. To remove the key, it is then rotated back to its insertion position, and the lost motion between the plug and the component  80  allows the plug to rotate relative thereto, thereby bringing its projection  82  back to its original key insertion state, as shown in FIG.  20 . The key is then removed and the door closed on exit in the normal manner thereby automatically deadlocking the closed door as previously described. Pivoting of the handle is now prevented by the blocking lug  81 . 
     To open the door from the outside, the key is inserted in the plug of the assembly  28  and turned in a clockwise direction as viewed in FIG. 20, the locking bar  28   b  of this assembly  28  engaging through the cam slot  114  extending into said bore of the component  80  having said V-shaped projections  80   a  therein. With the cam  99  in its FIG. 6 position, the disposition of the slot  114  relative to said V-shaped projections in the bore in one end of the component  80  is such that when the key is turned there is initial take-up of lost motion between the bar and respective engagement sides of the V-shaped projections, this lost motion corresponding to the movement of the driving surface  98  into engagement with the foot  96 . Once this lost motion has been taken up and the cam is at the position shown in full in FIG. 10, continued turning of the key effects turning of the locking bar  28   b , which, by virtue of its engagement with respective surfaces of the V-shaped projections  80   a  causes the component  80  to rotate from its FIGS. 20 and 32B positions to its FIGS. 22 and 32A positions where the lug  81  is clear of the projection  88  on the handle. This is an important safety aspect of the re-entry procedure in that it releases the locking of the handle which was effected upon original egress. As a result, once the door is thereafter closed, it can (immediately) be re-opened from the inside by pivoting the handle. The described key rotation also effects angular movement of the cam to retract the bolt as shown in FIG. 10 in phantom. Again as the component  80  moves from its FIG. 20 to its FIG. 22 position, the spring loaded ball partly received in bore  87  moves out of partial engagement in recess  85  to partial engagement in recess  86  to hold the component  80  in its FIG. 22 position. Thereafter the key is turned back to its insertion position (FIG.  32 B), resulting in the locking bar also moving relative to the component  80  due to the lost motion provided, so that the key can then be removed from the plug of the assembly  28  once the door has been opened and the bolt again held in its retracted position. The handle is now again operable when required to effect retraction of the bolt. It will be appreciated that with the handle blocked against angular movement, access to the fixing screw  27  for the screwdriver shank  27   a  through the cut-out in the end of the handle is prevented, and thus removal of the assembly of casing part  11  and plate  12  is prevented. 
     Finally with regard to operation of the lock, reference is made to the use of the snib  106  as shown in FIGS. 13 to  15 . 
     As previously described, operation of the handle  36  or the cam  99  to retract the bolt  55  will bring it to the positions shown in FIGS. 13 and 15 respectively where the foot  97  of the plate  93  of the bolt is spaced from the interior surface of the end wall  14 . In this position, as shown in FIG. 13, the spring loaded snib  106  is out of alignment with the hole  103  in said plate  93 , and thus cannot be operated to retain the bolt in its retracted position irrespective of the state of the bolt release member  69 . However if the bolt is pushed inwardly from its leading end at the outer edge surface of the door, it can be moved to its FIG. 14 position where the clearance between the foot  96  and the wall  14  is taken up so that the foot now abuts the interior surface of said wall. In this position the hole  103  has now become aligned with the snib, which can thus be pressed inwardly against its spring bias so that its end part  109  is received through said opening, removal of the inwards force on the bolt resulting in the bolt automatically being moved by its spring force in a direction to extend from the casing. However although the bolt can move by said amount of clearance away from the wall  14 , further movement is stopped by the engagement of an edge of the hole  103  engaging the part  109  of the snib, as shown in FIG. 15, so that the snib is held thereby to retain the bolt in its normally retracted position. The door can thus now be open and closed without the bolt automatically shooting or needing to be withdrawn. 
     With conventional snib locking arrangements of this type, for example where the snib is slid between engagement and non-engagement positions respectively to hold the bolt, it is possible for the snib inadvertently to be disengaged and thus allow inadvertent shooting of the bolt and resultant inadvertent locking of the door. In contrast, with the present arrangement, inadvertent release of the snib is very unlikely in that specific positive action is needed at the front edge surface of the door, namely the application of pressure to the end of the bolt to force it inwardly to an extent where the hole  103  is again fully aligned with the snib which then would automatically release under its spring bias, the bolt then automatically moving to its normal retracted position. As mentioned, the snib could be arranged with the bolt, so that the bolt is held by the snib slightly inwards of its FIGS. 13 and 15 position, but slightly outwards of its FIG. 14 position. 
     Finally in relation to consideration of pressure being applied to the end of the bolt, it will be noted that any attempt forcibly to retract the bolt from its FIG. 3 position, for example by inserting an implement between the end of the bolt and its keeper, would result in a force being applied to the deadlock element  44 . With some lock arrangements, the application of such a force to the deadlock might cause it to release from the bolt which can then be forced inwardly to unlock the door. However with the present arrangement the housing  38 , as described, provides the upper half of the bearing for the rod  43  of the deadlock element. Additionally, however, this housing provides a solid wall  238  immediately adjacent the side of the rod remote from the body part  45  of the element  44 . Since the housing  38  is secured to the casing by fixing screws, any inward force applied to the bolt in its FIG. 3 position and received by the deadlock element  44  will be taken by said adjacent solid wall of the housing  38 , and since this is securely fixed to the casing, there is resistance to disengagement of the deadlock member from its engagement with the bolt, thereby making the bolt more secure against such attack. 
     Although in the embodiment of the lock described, blocking of the handle can only be actuated from inside of the door, in an alternative embodiment means could be provided within the lock casing to allow for blocking of the handle to be actuatable from outside of the door, in addition to, or instead of, from the inside of the door. Such means could be the same as or different from the means used inside the door, and moreover whilst it would be convenient for any means operable from outside of the door to be operated by the key, so that for example the key could be used both to engage and retract the blocking member, this may not necessarily be the case, so that something other than key operation could be provided at the outside of the door to cause said blocking, and similarly something other than key operation could be provided at the inside to cause said blocking. However most preferably, the blocking would be actuatable from both inside and outside the door, preferably in both cases by means of the key of the lock. 
     In another embodiment means other than the outside key operation which deactivates the blocking means, such as an outer handle, could be used to retract the bolt.