Abstract:
Designs for adapting a ladder rail so that accessories to the ladder can be quickly and securely mounted and released without using tools. Aspects of the invention include attachment bases permanently mounted to the ladder rail with structures for toolless attachment and release of accessories to the base, including guide lips that allow the accessory to be easily removed.

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS 
     The present application is a continuation-in-part of U.S. patent application Ser. No. 10/697,674 filed 29 Oct. 2003 entitled QUICK RELEASE FOR LADDER LEVELERS now U.S. Pat. No. 7,036,633 which claims priority from U.S. provisional patent applications, Nos. 60/549,195 and 60/577,048, respectively filed 1 Mar. 2004 and 3 Jun. 2004; and is a continuation-in-part of U.S. patent application Ser. No. 11/142,080 filed May 31 2005 now abandoned entitled ACCESSORY ATTACHMENT SYSTEM FOR A LADDER, AND METHODS; and claims priority from U.S. provisional patent applications 61/137,506 filed Jul. 30, 2008 and 61/217,491 filed Jun. 2, 2009. 
    
    
     BACKGROUND 
     Extension ladders, combination ladders, and stepladders consist essentially of two rails with rungs between the rails. Various accessories, for example levelers, wheels, tool or paint can hooks and plank support brackets, can be attached to the ladders to help one work from the ladder. Each of these accessories typically has its own method of attachment to the ladder, for example releasably hooking onto the rungs or securely held to the rails by bolts placed through holes specially drilled into the rails and threaded into a nut or receptacle of the accessory. 
     For example, for many types of ladders it is useful to have a leveler at the bottom of one leg or both legs. The leveler effectively adjusts the length of the bottom of the leg so that the ladder will go straight up from uneven ground or from different treads in a staircase. For safety, levelers are preferably securely bolted to the rails of the ladder or a static portion of the leveler may be integral with the leg of the ladder. 
     For ladders that are often used without an accessory, it is undesirable to have the extra weight of the accessory always present. Although accessories have been designed that quickly attach to rungs of a ladder or slip over the bottoms of the rails to achieve a quick attachment and release feature, these attachments are not sufficiently secure and include protrusions that catch on objects, damaging the object or the protrusion or creating a hazard. 
     SUMMARY OF THE INVENTION 
     The invention is a way of adapting a ladder rail so that accessories to the ladder can be quickly and securely mounted and released without using tools. Aspects of the invention include: (1) novel configurations of holes in ladder rails for receiving accessories for toolless attachment and release; (2) novel catches affixed to the rail to secure the accessory; (3) novel attachment bases permanently mounted to the ladder rail with structures for toolless attachment and release of accessories to the base; (4) novel catches affixed to the base to secure the accessory; (5) novel attachment structures on the accessory for toolless attachment and release of the accessory to a base or a ladder rail; and (6) novel catches affixed to the accessory to secure the accessory to a base or rail. 
     In one aspect of the invention, a ladder includes a rail, the rail being essentially an I-beam with a web connecting the beam portion that is most in compression with the beam portion that is most in tension. The web may be adapted so that the accessory can be placed in contact with the web and then slid along guides that restrict movement, or pivoted around one or more engaging hooks that restrict movement, until it seats in engagement with the web whereupon a catch secures the accessory. The adaptation may be directly in the web or in an attachment base affixed to the web. 
     The guides along which the accessory may be slid may be slots cut into the web or base or channels formed by adding material to an outer surface of the web or base, in which case insertion gaps may cut into outer walls of the channels to allow flanges or tabs of the accessory to be inserted into the channels. 
     The catch may be affixed to the ladder or attachment base or it may be affixed to accessory. If affixed to the accessory, it may be a spring loaded latch on the accessory that catches a hole in the web or base or other surface of the ladder that is generally perpendicular to the direction of movement of the accessory that would allow release of the accessory. If affixed to the ladder, it may be affixed to an outer surface of the web or to an inner surface or to a rung. If affixed to an inner surface of the web or to the base, it may act on a pin of the accessory inserted through a hole in the web or base. To retain the accessory, the catch may prevent the pin (such as a knob or an L-hook) from moving parallel to the surface of the web or base or it may prevent the pin from being retracted out of the hole, such as by fitting into a recess in a side of the pin, which recess might be a hole through the pin. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       The features of the present invention which are believed to be novel are set forth with particularity in the appended claims. Aspects of the invention may best be understood by making reference to the following description taken in conjunction with the accompanying drawings wherein: 
         FIG. 1  is an exploded, perspective view of a ladder system that incorporates a ladder accessory releasably attachable to keyhole shaped slots in a ladder rail. 
         FIG. 2  is a cross-sectional view of the ladder accessory in  FIG. 1  releasably attached to the ladder. 
         FIG. 3  is an exploded, perspective view of a ladder system that incorporates a ladder accessory with L-hooks releasably attachable to oval shaped slots in a ladder rail. 
         FIG. 4  shows side-by-side rows of pairs of slots. 
         FIG. 5  shows a ladder-mount for an accessory where the ladder-mount includes one or two right angle hooks at one end or edge and an inserted pin type catch. 
         FIG. 6  is a side view of a ladder rail showing a pattern of four holes for attaching accessories. 
         FIG. 7  shows a rail with a butterfly hole in the web configured for accessories to be locked to the rail by rotation into engagement. 
         FIG. 8  shows a butterfly knob for insertion into the butterfly hole. 
         FIG. 9  is a cross-section view of a prior art ladder rail. 
         FIG. 10  is a cross-section view of a ladder rail with flanges added to form a pair of opposing channels to which accessories may be attached. 
         FIG. 11  is a side view of an accessory attachment plate that fits into the channels formed by added flanges. 
         FIG. 12  is side view of the ladder rail with added flanges and cut outs in the flanges. 
         FIG. 13  shows the quick attachment components built into base unit that may be permanently bolted to a ladder rail so that quick attachment holes do not need to be cut into the ladder and it shows a catch in the form of a spring loaded latch. 
         FIG. 14  shows the base unit bolted to a ladder and an accessory quick-connected to the base unit. 
         FIG. 15  is an oblique view of the inside of a ladder rail with an affixed catch in the form of a spring loaded latch. 
         FIG. 16  shows an alternative latch that pivots to one side instead of away from the web. 
         FIGS. 17 and 18  shows an alternative latch that is slid parallel to the surface of the web to allow a knob on a pin to be slid in an opposite direction for release. 
     
    
    
     DETAILED DESCRIPTION 
     In the following detailed description of exemplary embodiments of the invention, reference is made to the accompanying drawings. The detailed description and the drawings illustrate specific exemplary embodiments by which the invention may be practiced. Other embodiments may be utilized, and other changes may be made, without departing from the spirit or scope of the present invention. The following detailed description is therefore not to be taken in a limiting sense, and the scope of the present invention is defined by the stated claims. 
     Keyhole Slots 
       FIG. 1  is an exploded, perspective view of a ladder system  18  according to an embodiment of the invention. The ladder system  18  includes a ladder  20  and a ladder accessory  22  releasably mounted to the ladder  20 . The ladder  20  includes a ladder-accessory mount  24  (eight shown but only one indicated with the reference number  24  for clarity), and the ladder accessory  22  includes a ladder mount  26  (a portion of the accessory) that one can couple to the ladder-accessory mount  24  to releasably attach the ladder accessory  22  to the ladder  20 . The ladder  20  also includes two rails  28  which are comprised of beams with a web connecting the structural elements that experience the most tension and compression. The web in each rail has an outer surface  33  and an inner surface  35 . Rungs  30  are disposed between the webs and attached at the inner web surfaces  35 . Each rail  28  includes an end  32 . 
     As shown in  FIG. 1 , each rail  28  may incorporate one or more ladder-accessory mounts  24  as desired. Each accessory mount may be made simply by placing holes in a defined pattern in the web or by affixing an accessory mounting base, as shown in  FIGS. 13 and 14 , which has attachment structures. Each mount may comprise a set of slots or holes or opposing channels as further explained below. A particular accessory may use all holes or slots or channels in a single mount or it may use less than all or it may use part of one mount an part of another mount. The slots or holes or channels may be disposed on the outer surface of the web of each rail in such a way that they are continuously and evenly spaced along the entire web and the web is all one very long mount, only a small part of which is used by any one accessory. 
     Examples of accessories that may be attached include a wheel  36  for ease of transporting the ladder, shown in  FIG. 1 , a ladder platform, a ladder jack, a V-rung and hook, a safety cinch strap, a carriage and ski, a hook, a standout bracket, a stabilizer, and a leveler (shown in  FIGS. 3 and 7 ). 
     The ladder-accessory mount  24  may comprise any combination of slots, holes, or opposing channels that that can be used by pins or knobs or hooks or flanges of a ladder-mount  26  portion of an accessory  22  to cooperate with each other to releasably attach the ladder accessory  22  to the ladder  20 . For example, as shown in  FIG. 1 , the ladder-accessory mount  24  may include three keyhole slots  38 , and the ladder mount  26  may include three knob protrusions  40  that mate with a respective one of the slots  38  to restrain movement of the ladder accessory  22  relative to the rail  28  in five of six directions  42   a ,  42   b ,  44   a ,  44   b ,  46   a  and  46   b , The direction  42   a  is up along the rail  28 , and the direction  42   b  is opposite the direction  42   a  or down along the rail  28 . The direction  44   a  is perpendicular to the directions  42   a  and  42   b , and right, along the width of the rail  28 , and the direction  44   b  is opposite the direction  42   a  or left along the width of the rail  28 . The direction  46   a  is perpendicular to the directions  42   a ,  42   b ,  44   a  and  44   b , and out away from the rungs  30  of the ladder  20 , and the direction  46   b  is opposite the direction  46   a  or toward the rungs  30  of the ladder  20 . 
     Still referring to  FIG. 1 , the outer web surface  33  or outer mounting base surface may include a catchment surface which in  FIG. 1  is a hole  50  which is acted against by a catch or latch on the accessory to secure the ladder accessory  22  to the outer web surface  33 . For example, in one embodiment the ladder mount  26  of the ladder accessory  22  includes the spring latch  48 . The spring latch  48  includes a locking pin (not identified with a reference numeral) that may be inserted into the hole  50  in the rail  28 . The spring latch  48  restrains movement of the ladder accessory  22  relative to the rail  28  in the sixth direction (here direction  42   a  or up) when the ladder accessory  22  is releasably attached to the rail  28 . Thus, the spring latch  48  secures the ladder accessory  22  to the ladder  20 . In applications when the weight of the ladder accessory  22  or the pressure exerted on the accessory  22  from a tool, material or user supported by the accessory  22  sufficiently restrains the accessory from moving relative to the rail  28  in the sixth direction  42   a , the spring latch  48  may be omitted or not used. However, when the spring latch  48  is used in such applications, the spring latch provides additional security against the ladder accessory being accidentally released from the ladder  20 . 
     In operation, one releasably attaches the ladder accessory  22  to the ladder  20  by coupling the ladder mount  26  portion of the accessory  22  with the ladder-accessory mount  24  on the ladder rail or mounting base. For example, in one embodiment one inserts each protrusion  40  into a respective one of the slots  38 . Then one moves each protrusion up or in the direction  42   a , or down or in the direction  42   b  (here down) inside the slot  38  to insert each protrusion  40  into the narrower portion  49  of the respective keyhole slot  38 . Contact between one or more of the protrusions  40  with the narrower portion  49  of respective keyhole slots  38  restrain movement of the ladder accessory  22  relative to the rail  28  in the directions  42   b ,  44   a ,  44   b ,  46   a  and  46   b , With each protrusion  40  inserted in the narrower portion  49  of the respective slot  38 , the locking pin of the spring latch  48  is aligned with hole  50  and urged into the hole. To remove the ladder accessory  22  to replace it with another one, one removes the accessory  22  by withdrawing the locking pin from the hole  50 , moving the protrusions  40  up or in the direction  42   a  relative to the rail  28 , and withdrawing each protrusion  40  from the respective slot  38 . The latch  48  in  FIG. 1  may be withdrawn from the hole  50  by pulling on the base of the pin from the accessory side or by pushing on the head of the pin from inside the ladder rail. 
       FIG. 2  is a cross-sectional view of the ladder accessory  22  releasably attached to the ladder  20 . 
     Each protrusion  40  and slot  38  may be configured as desired to restrain movement of the ladder accessory  22  relative to the ladder rail  28  when a protrusion  40  is inserted into a respective one of the keyhole slots  38 . For example, in one embodiment each protrusion includes a knob  52  and each slot  38  includes a narrower portion  49  ( FIG. 1 ). The knob  52  includes contact surfaces  54   a  and  54   b , and each slot includes contact surfaces  55   a  and  55   b , When a protrusion  40  is inserted into the narrower portion  49  of a respective slot  38  and pressure is exerted on the ladder accessory  22  in one or more of the directions  42   b ,  44   a  and  44   b , the contact surfaces  54   a  and  55   a  contact each other to restrain movement of the ladder accessory  22  relative to the rail  28 . And when pressure is exerted on the ladder accessory  22  in the direction  46   a , the contact surfaces  54   b  and  55   b  contact each other to restrain movement of the ladder accessory  22  relative to the rail  28 . Movement of the ladder accessory  22  relative to the rail  28  in the direction  46   b  is restrained by contact between the rail  28  and the ladder accessory  22 . Movement of the ladder accessory  22  relative to the rail  28  in the direction  42   a  is restrained by the spring latch  48 . 
     Still referring to  FIG. 2 , the spring latch  48  may automatically lock the ladder accessory  22  to the ladder  20 , when the ladder-accessory mount  24  is coupled to the ladder mount  26 . For example, in one embodiment the spring latch  48  includes a locking pin  56  that may be inserted into the hole  50  of the rail  28 , a housing  58  attached to the ladder mount  26  and having a wall  60 , and a spring  62  to urge the locking pin  56  away from the wall  60 . When the locking pin  56  is aligned with the hole  50 , the spring  62  urges the locking pin  56  into the hole  50 . Thus, when the ladder accessory  22  is moved in the up direction  42   a , the rail  28  contacts the locking pin  56  to restrain movement of the ladder accessory  22  in the up direction  42   a , Alternatively, a non-spring loaded catch may be used, such as a pin manually inserted into holes in the accessory and the rail that line up when the accessory is mounted. 
     Oval, Rectangular, and Butterfly Slots 
       FIG. 3  shows an embodiment where the rails have oval slots  37  along a centerline of the web and the accessories have L-hooks  39 . The L-hooks each have an inner ledge  45  that presses against the web to restrain movement of the hook away from the web. The L-hooks are inserted into the slots and the accessory is slid along the rail so that the accessory is secured by the ledges on the hooks against movement in all directions but one, along the rail. A catchment device on the accessory, which may be a spring latch or may be a non-automatic catch, catches a catchment surface on the ladder to secure the accessory. The catchment surface may be one of the slots with no hook inserted, or it may be a slot into which a hook is inserted, such as the bottom-most slot in  FIG. 3 . After the hooks are slid into engagement, a portion of the bottom slot that was occupied as the hook was inserted is now available for use. A catch  47 , as shown in  FIG. 3 , may be inserted into this empty portion of the slot, beside the base of the hook. In  FIG. 3 , the catch  47  is shown in inserted position, not in retracted position. The catch  47  may be a spring-loaded latch or it may be a manually actuated catch. 
     In the oval-slot system shown in  FIG. 3 , because the slots are symmetrical up and down, any accessory can be attached in either an up orientation or a down orientation, which is an advantage for accessories that have no single up or down orientation such as a transport wheel as shown in  FIG. 1 . 
     Described above are keyhole slots and oval slots. Other slot shapes are possible, particularly rectangular slots and butterfly slots  238  (oval slot with superimposed round hole of larger diameter than the width of the slot). Each slot needs to be at least wide enough across a width of the web to receive L-hooks or knobs of adequate thickness to have adequate strength. A preferred oval slot width is ⅜ to ½ inch. However, if the L-hooks are made of strong metal, the slots may be as narrow as 1/10 th  inch. The preferred slot length is about 1 inch, which allows ½ inch of hook ledge  45  support length against the inner web surface  35  after ½ inch of sliding travel in the slot and leaves a ½ inch opening for a catch to be inserted. The minimal slot length is about ½ inch long with ¼ inch of sliding travel in the slot and ¼ inch of purchase by the ledge  45  against the web surface  35 . 
     Whether the slots are oval shaped or keyhole shaped or butterfly shaped or rectangular, they can be distributed evenly along the ladder rail to allow an accessory to be attached anywhere or they can be place only in particular spots on the rail so that accessories will not be placed inappropriately. So that the rail retains adequate strength, the slots should not be placed no closer than about ½ inch from a rung attachment point or closer than about ½ inch from each other. It is preferred to place the slots at least 1 inch away from rung attachments and at least 1 inch away from each other. By selecting a stronger web material, the holes may be placed as close as ⅛ inch from a rung. 
     So that the accessory will be strong against rotation of a knob or L-hook in a slot, each accessory must engage at least two holes in the rail, either or both of which may be a slot. For this reason, each location on the rail where an accessory mount  24  is desired, there must be at least a pair of holes at a defined distance apart between 1 inch and 30 inches apart. The appropriate distance is controlled by the distance between structures on the accessory&#39;s ladder-mount  26  that engage the two holes of the pair. It is preferred that the holes in the pair are both between sequential rungs and therefore not more than about 10 inches center to center. In a preferred embodiment, there are 3 holes, the outer two holes forming the described pair at 9 inches center to center and an extra hole between them at 4½ inches center to center from each outer hole to provide additional strength. 
     Instead of one row of slots on the centerline of the web as shown in  FIG. 3 , there may be two rows of slots as shown in  FIG. 4  where each slot is one of a side-by-side pair of slots that are even with each other across the width of the web. Each slot in a first row of slots  41  is opposite a slot in a second row of slots  43 . The slots are preferably about ⅛ inch wide and about one inch long. The accessory has preferably four or more L-hooks that fit into the slots. The L hooks may be made at low cost and light weight by starting with a ⅛ inch thick sheet of metal, cutting it into a rectangle with L-hooks sticking off two opposite sides at locations symmetrical about a line on a centerline between the hooks, and then bending the metal 90 degrees at or near the base of each L-hook so the hooks now form pairs that are parallel to each other. The accessory is affixed to this sheet with four or more L-hooks. 
     Right Angle Pivoting into Engagement 
     As shown in  FIG. 5 , instead of using slots and sliding the accessory along the rail to seat it, the rail may have a pattern of round (or square or any other shape) holes and the ladder-mount  260 ,  262  portion of an accessory may have one or two (or more) right-angle shaped hooks at one end or side of the accessory as shown in  FIG. 5 . With the accessory at 90 degrees from its final mounted orientation, the right-angle hook(s)  256  are inserted into a hole (which may be a slot) and the accessory is pivoted 90 degrees about a pivot axis parallel to the surface of the web until the accessory reaches its mounted position at which point the right-angle hook(s) hold one edge or end of the accessory snug against the web. As shown in  FIG. 5 , the pivot axis is formed by an inside right angle  255  of the right angle hook  256  that fits into a hole in the rail. 
     For the system where accessories have a right-angle hook on one edge or end as shown in  FIG. 5 , a preferred pattern of holes in the ladder rail web is shown in  FIG. 6 . The accessories are designed with two right-angle hooks  256  and the two hooks are inserted into two holes  51  which form a pivot axis about which the accessory is pivoted until a pair of pins  250  in  FIG. 5  slides into a second pair of holes  53  in the web. The pivot axis formed by the pair of holes  51  is across the web. Alternatively, by appropriate design of the accessory, the pivot axis may be along the web, in which case the two right-angle hooks are farther apart and they are inserted into one of the holes  51  and one of the holes  53 . 
     Instead of two holes  51  side-by-side, there may be one hole that is rectangular or oval in shape to form the pivot axis. Alternatively, there may only be one round hole such that the accessory can pivot in all directions about the hole (rather than an axis) until the accessory is swung into locking engagement by at least one pin  250 ,  265  passing into at least one hole in the rail and catching the rail. The pin may be a fixed part of the accessory or it may be a removable part. 
     Catchments that retain the pin(s)  250  may be retractable nibs  251  as shown in  FIG. 5 . These nibs are a well known feature of locking pins. They are metal balls that are locked into protruding position by a spring loaded rod that passes through the center of pin  250 . When a protruding button on the end of pin  250  is pushed, the balls are released to retract into the pin. 
     Rotation into Engagement 
       FIG. 7  shows a rail configured for accessories to be locked to the rail by rotation into engagement. A butterfly knob  240  fits into a butterfly hole  238  in a rail or in a mounting base affixed to the rail. The butterfly hole is an oval slot superimposed with a hole at its center which hole has a larger diameter than the width of the slot. When the butterfly knob is inserted into the butterfly hole and rotated a bit, all parts of the accessory are restrained against movement with respect to the ladder rail in all directions except rotationally in a curved or polar direction  254   a - 254   b  about an axis  220 . The butterfly pin is inserted with the accessory at about 90 degrees from its final position and the accessory is then rotated into position. When a locking pin  132  is engaged, movement in the polar direction about the axis is restrained. The locking pin  132  may be replaced with a pin  250  having retractable nibs  251  as shown in  FIG. 5  so the nibs can add strength against forces tending to separate the accessory  184  from the rail. 
     Channels on an Outer Rail Surface 
     Instead of cutting holes in the ladder rail or mounting base, accessory attachment structures may be added to the rail or mounting base. An example is shown in  FIGS. 10 and 12 .  FIG. 9  shows a cross section of a prior art ladder rail which is a beam with an inner web surface  35  and an outer web surface  33 . In  FIG. 10 , flanges  310  and  312  have been added parallel to the outer web surface  33  to form channels  302  and  304  which are opposite each other and parallel to each other. Each channel is formed by a portion of the outer web surface  33  and a parallel surface of the flange  308 . Essentially identical channels may be form in a mounting base that is affixed to the rail. The base may be made by extrusion, such as of metal or composite fiber and resin or thermoplastic polymer. 
     To securely engage the rail or base, an accessory is provided with a ladder-mount as shown in  FIG. 11 . The ladder-mount has two tabs or flanges  314  that fit into channel  308  and two flanges  316  that fit into channel  302 . Each pair of flanges on the ladder-mount has a gap  318 ,  320  between the pair of flanges. The rail flanges  310 ,  312  also have gaps  322  shown in  FIG. 12 , each gap at least as wide as a ladder-mount flange so that the ladder-mount flanges can pass through the rail flange gaps  322  to allow the ladder-mount flanges to slide into the channels. As the flanges  310  and  312  are added to the parts of the rail beam that are most in tension or compression, they add significant strength to the rail. Consequently, the gaps  322  are not cut in the parts of the rail most likely to fail which are parts near the rung attachments  30 . 
     Where the flanges  310  and  312  are a part of an attachment base affixed to the ladder rail, it is unnecessary to cut away gaps  322  and it is unnecessary to include gaps  318  in the ladder-mount because the accessory flanges  314 ,  316  can be slid in the attachment base at an end of the attachment base. 
     Once the ladder-mount flanges are slid into the channels, the accessory is locked in place with a catch that catches a catchment surface on the rail that is perpendicular to the length of the rail. The catchment surface may be a hole in the rail  326  or it may be an edge  324  of the gap  322  in the rail flange  310 ,  312 . The catch may be a spring latch or a non-automatic catch. 
     Metal or Fiber Composite Ladders 
     Ladders that are adapted as described above for attaching accessories may be made of metal, such as extruded 6063-T52 aluminum, or fiber-resin composite such as fiberglass used for ladders. The holes, slots, and flanges described above may be applied to either material. However, for fiber composite materials, it is sometime preferred to carry a part of the load of an accessory on a metal plate attached to the web such as with rivets. In this case, the holes or slots are formed in both the web of composite material and in the attached plate. 
     Bolt-On Accessory Mounting Base 
     Instead of being placed directly in the web of the ladder rail, the accessory attachment structures described above may be placed in a separate piece of material that is bolted or riveted to the rail. An example of such a bolt-on accessory attachment mounting base  80  is shown in  FIG. 13 . The dimensions should be at least one inch by six inches to insure adequate rigidity in its connection to the ladder rail and to the accessory, preferably at least 1 inch by 8 inches. In one embodiment, the dimensions of the attachment base are one and one-half inch by 12 inches. The attachment base need be only as thick as necessary to perform all of its functions, including spacing a leveler out from the side of the rail to clear a foot on the bottom end of the rail. A preferred embodiment is made of 6063-T52 aluminum rectangular tubing with one-eighth inch wall thickness. 
     As shown in  FIGS. 13 and 14 , the attachment base may be made in box beam shape for strength, at least 6 inches in length, hollow inside, with four side walls, each at least 1/10 inch thick, a first side and an opposite second side each being at least 1 inch in width. One adds holes in the first side of the box-beam through which the base is affixed to the ladder rail, and holes in the second side of the box-beam through which an accessory may be attached. It is preferable for the holes on the first side to be opposite holes on the second side for ease of attaching the base to the ladder. 
     The box-beam may be made of metal or it may be made of composite fiber and cured resin or of thermoplastic polymer. It is preferably extruded but it may be made by other methods such as cutting, bending and welding a plate of metal. If made by extrusion, it is attractive for the structures for attachment to comprise a pair of opposing channels into which tabs on the attachment may be slid as described above and shown in  FIGS. 11 and 12 , with or without gaps through which tabs may pass to enter the channels. 
     The accessory mounting base may be made by molding, with molded structures on a side of the molded material to which an accessory may be attached. The structures may be any of those described above. The base may be molded of thermo-plastic polymer, with or without added fibers for strength; it may be molded of composite fiber and resin; and it may be molded of metal. 
     Alternative Catches 
     The hand-releasable catch may be placed on the ladder rail or bolt-on accessory mounting base or on the accessory.  FIG. 13  shows an example where the catch is a spring  90  loaded latch  86  on a bolt-on accessory mounting base  80 . The latch pivots about an axis parallel to the web surface and perpendicular to the web length, the axis formed by a hinge pin  96 . As shown in  FIG. 14 , the latch  86  catches the knob  84  on one side  88  of the knob to restrain sliding movement of the knob. 
       FIG. 15  shows a similar hinged spring latch  401  modified to mount on the inside face  35  of a ladder rail  28 . The latch  401  includes a hole  404  to capture the knob and carry its force over a semi-circle contact area and a large pedal  405  for easy finger actuation. The latch pivots on a hinge pin  406  and is urged into place by a torsion spring  402 . The latch is attached to a piece of extruded metal  414  added to the inside face  35  of the ladder rail  28 . The extruded metal  414  includes guide lips  403  that keep the knobs from flopping to one side, which facilitates removal of the knobs from the slots. 
     The latch of  FIG. 15  can be modified to be made of one piece spring steel, eliminating the hinge pin and torsion spring. A portion can be bent to form a pivot so that one pushes in, like in  FIG. 15  to release the knob, or it can be designed with rivet points on one side of the knob and bent to form a handle on the other side of the knob so that one pulls out to release the knob. 
     One may form a spring latch that is pulled out, away from the inner surface  35  of the rail  28 , using a finger-pull ring. 
       FIG. 5  shows a ladder mount  260  of an accessory (not shown) with a right-angle hook  256 . It has at least one pin  250  that fits into a hole (or pair of holes) such as holes  53  in  FIG. 6 . A recess in the side of the pin can be caught by a catchment surface of a catch which is slid along the inner surface  35  of the rail. The catch includes a keyhole slot so that the pin is retained when the catch is slid in one direction and released when the catch is slid in another direction. In one embodiment, the catch has two key hole slots side by side to retain two pins  250  simultaneously. 
       FIGS. 17 and 18  show a catch that must be pulled to mount the accessory and pulled again to release the accessory. A tab  281  is coupled to two parallel arms  285 , one extending on either side of a piece  286  affixed to the web  35  and on each side of the keyhole  38 . The tab and arms are held against a stop (not shown) by one or two springs  282 . On the keyhole side of each arm  285  is an indentation  284 . Into each indentation, when the tab is pulled to compress the springs, a ball bearing  283  may be pushed by the knob (or fall by gravity) to allow the knob to pass and be released. In  FIG. 21 , the latch assembly is covered with a cover  287 . 
     Although the present invention has been described in considerable detail with reference to certain embodiments, other embodiments are possible. Therefore, the spirit or scope of the appended claims should not be limited to the description of the embodiments contained herein. It is intended that the invention resides in the claims hereinafter appended.