A clasp fastener having a clasp (1) is designed to be snapped into engagement by exerting a closing force. A locking device (4) for locking the clasp (1) is placed by the closing force in an engaged position in which it is in a first snap engagement with a locking projection (6), and a closing member (5) for closing the clasp (1) is fixed by the closing force in a safety position in which it is in a second snap engagement with the locking device (4) so that the snapping force of the first engagement of the clasp (1) with the locking projection (6) is increased. At least one variable-diameter pin (17,18) that is flexible and/or has different diameters allows some movement of the locking device (4), so that the effective closing force exerted on the locking projection (6) is reduced.

FIELD OF THE INVENTION 
This invention relates to fasteners and more particularly to a safety clasp 
fastener for a watch strap or bracelet. 
BACKGROUND OF THE INVENTION 
Usually, straps of wrist-watches are opened and fastened by using known 
fastener devices like a buckle or a clasp. The application of one of these 
fastener devices depends often on the material from which the watch strap 
is made. For example, a watch strap made from soft material like leather 
is fastened by actuating a buckle. By contrast, a watch strap made from 
rigid or metallic material is often fastened by snapping a clasp. 
A watch strap having a buckle is fastened in several stages. First, an end 
portion of the watch strap is inserted into a first loop, then a tongue of 
the buckle is engaged in a strap hole and finally the buckle is fixed by 
inserting the end portion of the watch strap into a second loop of the 
buckle. The end portion is secured by sliding its end in a guide loop of 
the watch strap. A watch strap having a clasp, by contrast, is snapped in 
one or two stages by fixing the clasp to a stud of the watch strap. 
Hereinafter, discussion will be limited to the advantages and disadvantages 
of a clasp fastener of a watch strap. 
A clasp fastener is generally provided with an adjusted closing force. 
Usually, the closing force is regulated during manufacture and is 
adjustable by a specialist during maintenance of the watch strap. This 
force can differ in function of the watch strap model chosen. Models 
destined for male or sporting users are activated with a closing force 
higher than that of a model destined for female users. One disadvantage is 
that the closing force of a watch strap clasp cannot be regulated by users 
as a function of daily or leisure activities. 
A clasp fastener which is not provided with a security device for securing 
its fastening procedure, can, in accordance with the strength of the 
closing force, open as the result of a heavy shock, for example during a 
sport activity. One disadvantage is that a watch strap clasp having no 
security device cannot prevent unintentional fastener opening. 
SUMMARY OF THE INVENTION 
An object of the invention is to provide a clasp fastener with general 
application, for example for a wrist-watch, which has a particularly 
compact construction and is compatible with known, proven manufacturing 
methods. 
According to the invention, this object is achieved by a clasp fastener 
with a completely novel concept. The clasp fastener is made from elements 
which allow positioning and securing or safety engagement of the clasp and 
which allow individual regulation of the closing force. 
By a latching force, in a first stage, a locking device of the clasp 
carries out a positioning closure, i.e., the actuation of the locking 
device allows its positioning against a locking projection of the clasp 
(first snap engagement). In a second stage, a security cover of the clasp 
carries out a securing closure, i.e., the clasp is fixed by the securing 
cover (second snap engagement), increasing therefore the latching force of 
the first snap engagement of the clasp with the locking projection. 
Moreover, one or more variable-diameter pins of the locking device are 
provided, these pins having spring characteristics and/or different 
diameters for allowing some movement or clearance relative to one or more 
locking elements of the locking device, reducing therefore the closing 
force effectively exerted on the locking projection and allowing 
individual regulation of the closing force. 
Finally, the securing cover is mounted in a detachable manner about an axis 
of articulation of a hinge. One or more locking elements having straight 
and rigid portions constitute a resisting axis, which axis resists closure 
of the security cover in a closure plane. The one or more locking devices 
are adjustable with respect to the hinge, so as to be able to vary the 
mutual distance from the straight and rigid portions to the hinge for 
increasing or reducing the resisting force. This resisting force resists 
the securing closure of the security cover on the locking device, allowing 
individual regulation of the latching force.

DESCRIPTION OF PREFERRED EMBODIMENTS 
FIGS. 1a and 1b show a preferred embodiment of a clasp fastener, for 
example for a wrist watch, in a perspective view with a watch strap, in a 
closed state (FIG. 1a) and in an open state (FIG. 1b). FIG. 2 is a 
perspective, exploded view of the elements of the clasp fastener. The 
watch strap and the visible elements of the clasp fastener are preferably 
made from metal. They are, for example, constructed from stainless steel 
and/or gold. The partial views according to FIGS. 1a, 1b and 2 essentially 
show a clasp fastener, final links 2, 2' of the strap, a lower or base 
strip 3 of the clasp, a locking projection 6 mounted, for example by 
welding, on lower strip 3 of the clasp, a joining piece 7 which acts as a 
terminal connection element of the clasp, an upper strip 11 of clasp 1 and 
a locking device 4 provided with a securing cover 5 of clasp 1. With the 
knowledge of the present invention, a person skilled in the art can 
implement other embodiments of a clasp fastener. 
Clasp 1 is mounted in an openable manner about three articulation axes of 
three rods 8, 9 and 10 forming hinges. Rod 8 forms a hinge which allows 
articulation between upper strip 11 of clasp 1 and lower strip 3 of the 
clasp. Rod 9 forms a hinge which allows articulation between locking 
device 4 and a bushing 9.0 having a guiding function and being fixed to 
upper strip 11 of clasp 1. Rod 10 forms a hinge allowing articulation 
between securing cover 5 and locking device 4 and also between locking 
device 4 and final link 2' of the watch strap or bracelet. Clasp 1 can be 
latched closed by successive snap engagements of locking device 4 and 
securing cover 5 with locking projection 6. Completing the description of 
the visible elements, a rod 13 forms a hinge 13 allowing articulation 
between joining piece 7 and a final link 2 at the other end of the watch 
strap or bracelet. The axes of the rods forming hinges 8, 9, 10 and 13 are 
oriented more or less perpendicular to the general plane of the watch 
strap and to the opening and closure planes of clasp 1. With the knowledge 
of the present invention, a person skilled in the art can implement other 
arrangements of axes of a clasp fastener. 
According to one characteristic of the invention, the snapping mechanism of 
the watch strap clasp fastener operates by means of articulation elements 
which are activated in two engagement stages in a closure plane of clasp 
1. In a first stage, for example, by pressing an end portion of securing 
cover 5, upper strip 11 of clasp 1 is pivoted relative to final link 2' 
until upper strip 11 contacts against lower strip 3 of the clasp. At the 
same time, locking device 4 is pressed against lower strip 3 of the clasp 
until locking device 4 contacts locking projection 6 which protrudes from 
lower strip 3 through an opening in upper strip 11 of clasp 1. Locking 
device 4 is positioned by a first snap engagement against locking 
projection 6. In a second stage, securing cover 5 is pivoted relative to 
locking device 4 and pressed against locking device 4. Securing cover 5 is 
kept on locking device 4 by a second snap engagement. This second snap 
engagement increases the snapping force of the first snap engagement of 
clasp 1 with locking projection 6. Clasp 1 according to the invention is, 
therefore, engaged in a secured closure state. Details concerning these 
engagements are described in the description of FIGS. 5a to 5c, 6a, 6b and 
7. 
Securing cover 5 is a closure device of the clasp fastener and an adornment 
piece. The aim is to hide locking device 4 under securing cover 5. In the 
closed state of the clasp, securing cover 5 covers and hides locking 
device 4 more or less completely. Closed clasp 1 with an engaged securing 
cover 5 has a similar appearance as joining piece 7 and improves 
appearance. The presence of a crown on the external wall of securing cover 
5 leads to a further increase of the very attractive appearance of clasp 
1. 
The opening mechanism of the closed watch strap clasp is identical to the 
closure mechanism, the above described two stages simply must be reversed. 
The opening occurs by actuating locking device 4. According to a preferred 
embodiment, securing cover 5 is first lifted by placing a thumb or an 
index finger in a groove or recess 12 in the external wall of joining 
piece 7 and next to a crown on the external wall of securing cover 5, 
lifting the cover. With the knowledge of the present invention, a person 
skilled in the art can implement other arrangements of this kind of clasp 
fasteners. 
FIGS. 3a and 3b show a first preferred embodiment of a locking device 4 of 
a clasp fastener in a top plan view parallel with a longitudinal plane 
(FIG. 3a) and in a side elevation view showing a lateral profile (FIG. 
3b). FIG. 4a is a corresponding perspective, exploded view. Locking device 
4 comprises a case 4.0 with a central notch 16. Case 4.0 has through-holes 
14.0, 14.0' forming bushings aligned with each other and having a guide 
function for keeping axes of two locking elements 14, 14' aligned. Case 
4.0 is also penetrated by aligned holes 10.0, 10.0' for receiving rod 10 
coaxially with the holes (see the description of FIGS. 1a, 1b and 2). 
According to a preferred embodiment, two guide bushings 15, 15' support 
rod 9 of the hinge previously described in a guide bushing 9.0 welded on 
upper strip 11 of clasp 1 (see the description of FIGS. 1a, 1b and 2). 
With the knowledge of the present invention, a person skilled in the art 
can implement other arrangements of elements of a clasp fastener. For 
example, it is possible to realize a clasp fastener having only one 
locking element. 
According to the first preferred embodiment of a clasp fastener, the two 
locking elements 14, 14' are elongated contact bolts having contact forces 
exerted along an axis AA' (FIG. 4a). The locking elements comprise, for 
example, springs. The contacting force of locking elements 14, 14' is 
defined by the chosen dimensions (length, diameter, etc.) and by the 
materials chosen. Each locking element 14, 14' comprises a outer bolt 
14.1, 14.1' and an inner bolt 14.2, 14.2'. Outer bolts 14.1, 14.1' are 
each provided with a rounded and convex portion for contact purposes and 
with an elongated portion for sliding and pivot purposes. Inner bolts 
14.2, 14.2' are each provided with a rounded and convex portion for 
contact purposes. Outer bolts 14.1, 14.1' and inner bolts 14.2, 14.2' are 
joined in a way to resist compressive forces along their contact axis AA'. 
After mounting in case 4.0 of locking device 4, locking elements 14, 14' 
are guided by holes 14.0, 14.0' having a guidance function and being able 
to support external pressure exerted on outer bolts 14.1, 14.1' and on 
inner bolts 14.2, 14.2'. Locking elements 14, 14' are mounted in a 
detachable manner and with some movement or clearance along their contact 
axis AA'. Outer bolts 14.1, 14.1' protrude beyond two external walls of 
case 4.0, while inner bolts 14.2, 14.2' protrude inwardly beyond two 
internal walls of case 4.0. Thus, end portions of locking elements 14, 14' 
protrude beyond two external walls of locking device 4 on the side of 
contact with securing cover 5, while inner end portions of locking 
elements 14, 14' protrude beyond two internal walls of locking device 4 to 
make contact with locking projection 6. Once locking device 4 is engaged 
with locking projection 6, projection 6 is within central notch 16 in 
engaged contact with locking elements 14, 14'. After engagement of 
securing cover 5 with locking device 4, walls 22, 22' and recesses 20, 20' 
of securing cover 5 are in engaged contact with locking elements 14, 14'. 
A preferred embodiment of a securing cover 5 is shown in FIGS. 5a to 5c. 
Details concerning the functioning of locking elements 14, 14' are 
described with reference to FIGS. 5a to 5c. 
The stages of the closure and opening mechanism in a closure and opening 
plane of a first preferred embodiment of locking device 4 of a clasp 
fastener are shown in three different states in FIGS. 5a to 5c. FIGS. 5a 
to 5c are sectional views showing partly a locking projection 6, securing 
cover 5, and a locking device 4 having two locking elements 14, 14' 
mounted in two guide holes 14.0, 14.0' which keep the locking elements 
coaxial, the locking elements 14, 14' each having an outer bolt 14.1, 
14.1' and a inner bolt 14.2, 14.2'. 
FIG. 5a shows a first state of the closure stages. According to one 
characteristic of the invention, locking projection 6 welded on lower 
strip 3 of the clasp is provided with two fixing recesses 6.0, 6.0' having 
concave surfaces. Fixing recesses 6.0, 6.0' serve for snap engagement of 
the rounded, convex portions of inner bolts 14.2, 14.2'. Preferably, the 
concave surfaces of fixing recesses 6.0, 6.0' and the convex surfaces of 
inner bolts 14.2, 14.2' are shaped to match each other, having for example 
the same radius, allowing optimized contact due to a maximal contact 
surface between these two elements. With the knowledge of the present 
invention, a person skilled in the art can implement other embodiments of 
locking projections. 
FIG. 5b shows a second state of the closure stages wherein locking device 4 
is positioned by a first snap engagement with locking projection 6 (first 
closure stage). Locking device 4 comprises, with reference to FIG. 4, 
central notch 16 and inner bolts 14.2, 14.2' protrude through internal 
walls defining central notch 16. Under external pressures, locking 
elements 14, 14' are axially movable with clearance along their common 
axis AA'. They are received with clearance in holes 14.0, 14.0' which 
serve as guide bushings. Locking elements 14, 14' are kept correctly 
centered along the contact axes AA' and in the holes 14.0, 14.0' by 
elastic rings 21, 21', 21", 21'". These elastic rings are, for example, 
open spirals made from spring steel. In order to position locking device 4 
against locking projection 6, a first force or pressure is necessary for 
sliding inner bolts 14.2, 14.2' onto the outer borders of fixing recesses 
6.0, 6.0'. This first force pushes the locking elements 14, 14' slightly 
to the exterior of case 4.0 and compresses elastic rings 21', 21" situated 
next to inner bolts 14.2, 14.2'. After having passed the outer borders of 
the fixing recesses 6.0, 6.0', elastic rings 21', 21" expand and inner 
bolts 14.2,14.2' weakly latch with locking projection 6. The clasp 
fastener is engaged and positioned. This first closing force or closure 
pressure can be regulated by different means. According to the preferred 
embodiments, a strip 400 of locking device 4 contacts a contact element, 
for example, lower strip 3 of the clasp. This force can be varied by using 
variable-diameter pins. The actuation of locking device 4 against locking 
projection 6 and the variation of actuation forces of the clasp will be 
described in detail in the description of the second preferred embodiment 
of a clasp fastener according to FIGS. 6a, 6b and 7. 
FIG. 5c shows a third closure state wherein securing cover 5 is kept by a 
second snap engagement on locking device 4 (second closure stage). With 
reference to FIGS. 1a, 1b and 2 and to FIGS. 3a, 3b and 4a, 4b and 4c, 
securing cover 5 comprises two internal retaining recesses 20, 20' in side 
walls 22, 22' for engagement with outer bolts 14.1, 14.1' protruding 
through external walls of case 4.0. When securing cover 5 is closed over 
locking device 4, walls 22, 22' slide over outer bolts 14.1, 14.1' and 
push the locking elements 14, 14' slightly toward the interior of case 
4.0. This second force is chosen to be stronger than the resisting force 
of elastic rings 21, 21', 21", 21'". As shown in FIG. 5c, two elastic 
rings 21, 21'" situated next to outer bolts 14.1, 14.1' are compressed and 
that elastic rings 21', 21" situated next to inner bolts 14.2, 14.2' are 
extended. Inner bolts 14.2, 14.2' lock the fixing recesses 6.0, 6.0' of 
locking projection 6. After locking of outer bolts 14.1, 14.1' by 
retaining recesses 20, 20', the elastic rings 21, 21', 21", 21'" expand 
weakly. This second force or pressure increases the snapping force of the 
clasp and allows a safety fastening. With the knowledge of the present 
invention, a person skilled in the art can implement other embodiments of 
recess surfaces for successive engagements of a clasp. 
FIGS. 6a and 6b show a second preferred embodiment of a locking device 4 of 
a clasp fastener in a partly sectional outer plan view (FIG. 6a) and in a 
sectional side elevation (FIG. 6b). FIG. 7 is a transverse sectional view. 
Locking device 4 comprises essentially a case 4.0 with a central notch 16. 
Case 4.0 is penetrated by coaxial bore holes 17.0, 18.0 which perform a 
guide function for keeping variable-diameter pins 17, 18 along their axis. 
Moreover, case 4.0 has aligned through-holes 10.0, 10.0' for keeping along 
their axis a rod 10 of a hinge (see the description of FIGS. 1a, 1b and 
2). According to a preferred embodiment, two guide bushings 15, 15' 
support a rod 9 of a hinge in a guide bushing 9.0 welded onto upper strip 
11 of clasp 1. Two locking elements 14, 14' have the shape of elastic, 
auto-centered clips occupying a space 23 within locking device 4. Space 23 
is adapted for retaining locking elements 14, 14'. Once locking device 4 
is engaged with locking projection 6, the projection is within central 
notch 16 in engaged contact with locking elements 14, 14'. After elements 
14; 14' protrude beyond two internal walls of locking device 4 in the area 
of contact with locking projection 6. With the knowledge of the present 
invention, a person skilled in the art can implement other locking 
elements having similar locking characteristics. 
The mechanism of closure and opening of the second embodiment of locking 
device 4 differs slightly from the first embodiment with two locking 
elements 14,14' according to the description of FIGS. 5a to 5c. FIG. 7 
shows a locking projection 6 screwed into lower strip 3 of the clasp and 
having two fixing recesses 6.0, 6.0' which are concave surfaces of the 
outer wall of locking projection 6. Fixing recesses 6.0, 6.0' serve to 
permit snap engagement of the rounded and convex portions of locking 
elements 14, 14' having the shape of elastic, auto-centered clips. 
Preferably, the concave surfaces of fixing recesses 6.0, 6.0' and the 
convex surfaces of the locking elements 14, 14' are shaped to match each 
other, having for example the same radius allowing optimized contact due 
to a maximal contact surface between these two elements. When locking 
device 4 is positioned against locking projection 6, a first force or 
pressure is necessary for pushing locking elements 14, 14' into recesses 
6.0, 6.0'. Clasp 1 is engaged after this first closure stage. The safety 
closure occurs during a second closure stage, i.e., during a second snap 
engagement of securing cover 5 with locking device 4. With reference to 
FIGS. 1a, 1b and 2 and to FIGS. 3a, 3b and 4a, 4b and 4c, securing cover 5 
is engaged with locking elements 14, 14' engagement of securing cover 5 
with locking device 4, the walls of securing cover 5 are in engaged 
contact with locking elements 14, 14'. With the knowledge of the present 
invention, a person skilled in the art can implement other embodiments of 
elements of a clasp fastener. For example, it is possible to realize a 
clasp fastener having only one locking element. 
According to the second embodiment, two locking elements 14, 14' each 
having the shape of an elastic, auto-centered clip, are curved supports, 
supporting along a contact axis AA' and being provided with curved and 
more flexible portions 14.3, 14.3' and with straight and more rigid 
portions 14.4, 14.4'. These supports have rounded surfaces. Locking 
elements 14, 14' are, for example, springs. The contacting force of 
locking elements 14, 14' is defined by the chosen dimensions (length, 
diameter, etc.) and by the materials chosen. Preferably, the spring-like 
locking elements 14, 14' have no tension in their uncompressed positions. 
After mounting in case 4.0 of the locking device 4, locking elements 14, 
14' are guided in an adjustable manner by the walls delimiting space 23. 
The walls of case 4.0 being next to straight portions 14.4, 14.4' of 
locking elements 14,14' are, for example, guides. Under the influence of 
external pressures, locking elements 14, 14' are compressible/extendible 
along their contact axis AA'. End portions of locking elements 14, 14' 
protrude beyond two external walls of locking device 4 on the sides of 
contact with securing cover 5, while end portions of locking which 
protrude through external walls of case 4.0 and are compressed. This 
second force is chosen stronger than the resisting force of locking 
elements 14, 14' for thereby increasing the pressure against locking 
projection 6 and allowing a safety closure. The totality of these forces 
or pressures is controllable and variable. 
These forces or pressures can be regulated by different means. According to 
a preferred embodiment, case 4.0 contacts a contact element, for example, 
the lower strip 3 of the clasp. The closing force can be varied by means 
of variable-diameter pins 17, 18. According to one characteristic of the 
invention, these variable-diameter pins are adjustable by the choice of 
the used material, by the choice of the pin diameter, by the outer surface 
geometry, etc. These pins are, for example, soft or they have different 
diameters. FIG. 7 illustrates an example of two variable-diameter pins 17, 
18, wherein the central diameter of variable-diameter pin 17 is smaller 
than the central diameter of variable-diameter pin 18. Locking element 14 
is in contact with clearance with central diameter of variable-diameter 
pin 17, the locking element 14' is in contact with little or no clearance 
with the central diameter of variable-diameter pin 18. By a closing force, 
the diameter of variable-diameter pin 17 allows, therefore, a clearance 
for locking element 14, while the constant diameter of variable-diameter 
pin 18 allows little or no clearance with locking element 14'. Such a 
variation reduces the closing force effectively exerted on locking 
projection 6. With the knowledge of the present invention, a person 
skilled in the art can provide one or more locking elements having an 
equal closing force for the clasp. 
As a result, the closing force of a clasp provided, for example, with a 
pair of variable-diameter pins 17 (allowing a high variation) is lower 
than the closing force of a clasp provided with a pair of 
variable-diameter pins 18 (allowing a low variation). By using pins 18 
with a lower variation it is therefore possible to obtain models "Man" or 
"Sport" destined for male or sporting users are activated having a closing 
force higher than that of a model "Women" destined for female users and 
which are realized by using pins 17 with a reduced central diameter for a 
higher variation. The provision of one or more variable-diameter pins 17, 
18 is not restricted to a clasp 1 according to the second embodiment of a 
locking device 4. This kind of application of variable-diameter pins is 
also and without any problems possible for a clasp 1 according to the 
first embodiment of a locking device 4. 
The closing forces or pressures can be varied not only by using 
variable-diameter pins 17, 18 but they can also be varied by using other 
variation means. Another variation means represents the resisting force of 
locking elements 14, 14' exerted on securing cover 5 during a safety 
closure in a closure plane over a locking device 4. According to another 
characteristic of the invention, the orientation of locking elements 14, 
14' in space 23 of the second embodiment of a locking device 4 is 
adjustable. Locking elements 14, 14' can, for example, be rotated by 
180.degree. in space 23. The latter must be designed in a symmetric manner 
in locking device 4. Such a 180.degree. rotation allows variation of the 
mutual distances between straight portions 14.4, 14.4' of locking elements 
14, 14' and hinge rod 10. These straight and rigid portions 14.4, 14.4' of 
locking elements 14, 14' constitute a resisting axis oriented more or less 
perpendicular to the closure plane of securing cover 5. The resisting 
force of rigid portions 14.4, 14.4' exerted on securing cover 5 is 
increased or reduced as a function of the size of the distance between 
hinge rod 10 and the resisting axis. By rotating locking elements 14, 14' 
in space 23, it is therefore possible to vary, i.e., to increase or to 
decrease the resisting force exerted on the safety closure of securing 
cover 5. A change in orientation of locking elements 14, 14' in space 23 
according to FIG. 6a allows, therefore, a variation of the second snap 
engagement made by the securing cover 5. The first snap engagement made by 
the locking device 4 remains unchanged. The user can therefore adjust the 
safety force of clasp 1 in a free and rapid manner without consultation of 
a specialist, i.e., according to daily or leisure activities. 
The visible elements of the clasp are preferably made from metal, for 
example, from stainless steel and/or gold. According to one characteristic 
of the invention, and with reference to the description of FIGS. 1a, 1b, 
2, 6b and 7, locking projection 6 is mounted on lower strip 3 of the clasp 
preferably by welding or screwing. Other connection methods are naturally 
possible. Taking into account the high precision which is required for 
allowing easy and repeated operation of the clasp, and taking into account 
the difficulties resulting from the treatment of the chosen materials 
(reduced hardening after welding, asymmetric deformation after welding), 
preferably, welding is used for fixing a locking projection 6 made from 
gold on a lower strip 3 made from gold and screwing is used for fixing a 
locking projection 6 made from stainless steel on a lower strip 3 made 
from stainless steel. With the knowledge of the present invention, a 
person skilled in the art can provide fixation means for other base 
materials for example thermofusion for synthetic thermofusible materials.