Molded one-way snap fastener comprises a stud head having a base flange and radial fins extending up from its center to a circular top. The top has downward barbs spaced between the fins. The socket has a base flange and a sleeve having a tapered mouth with a throat and an annular downwardly and outwardly inclined bearing surface above the throat and a cylindrical opening thereabove. The dimensions of the parts are such that once the stud head is inserted into the socket and the barbs pass the throat, they spring out and contact the side walls of the cylindrical opening, immobilizing the stud head in the socket. After that, attempts to unsnap the socket result in the butting of the ends of the barbs into the bearing surface, which because of its downward and outward slope, spreads the barbs causing them more resolutely to defy unsnapping. The fastener must be destroyed to give up its snapped state.

BACKGROUND OF THE INVENTION 
1. Field of the Invention 
This invention relates to a one-way snap fastener, that is, a snap fastener 
which can be snapped closed but cannot be unsnapped without destroying it. 
Such fasteners are used, for instance, in attaching plastic strap 
bracelets to patients in a hospital. The purpose of such a bracelet is to 
identify the patient in a way which is reliable and cannot be defeated by 
its inadvertent or willful removal. 
More specifically, this invention relates to a one-way snap fastener in 
which the head presents a plurality of barbs which spring out after they 
snap together and then tend to spring out further and lock even tighter 
upon attempts to unsnap the fastener. 
2. Description of the Prior Art 
The prior art is of course replete with snap fasteners of different 
descriptions. There are, however, examples of permanently locking 
fasteners or one-way fasteners pertinent to the present invention. For 
instance, U.S. Pat. 3,416,200, which issued Dec. 17, 1968 to Daddona, 
discloses a fastener wherein the stud has a solid head and the socket has 
an upwardly inclined annular strut which catches under the head after the 
snap installation. There is ample room in the socket opening to permit 
tilting of the head. 
In U.S. Pat. No. 3,210,820, which issued Oct. 12, 1965 to J. H. Humiston, 
the head is split and squeezes together as it passes the neck of the 
socket. 
SUMMARY OF THE PRESENT INVENTION 
In the present invention the stud head has a solid top from the periphery 
of which downward barbs extend. The throat of the socket is substantially 
the same diameter as the barb top of the stud, and the opening of the 
socket beyond the throat is the same diameter as the outer diameter of the 
barbs to prevent lateral motion or "play" in the snapped-together 
assembly. Above the throat the socket is formed with a downwardly and 
outwardly slanting annular-bearing surface.

DESCRIPTION OF THE PREFERRED EMBODIMENT 
A stud head embodying the invention is generally designated 10 in FIG. 1. 
It, like the socket, is molded from a synthetic plastic such as Acetel. 
The stud head comprises a circular base flange 12 from the center of which 
extend upwardly a plurality of radial fins 14. The fins all extend into 
the center of the flange and are molded integrally. Where they join the 
base flange 12, the flanges are formed with a radially outward chamfer 16 
(FIG. 2), and above the chamfer each of the fins is formed with an outward 
nub 18. 
At the top of the fins is integrally molded a solid cylindrical head 20. As 
shown in FIG. 1, the head 20 is formed in between the fins 14 with 
downward barbs 22. Barbs 22 extend freely and straight downward, thinning 
as their lower ends are approached and they terminate in a distal end 24. 
As shown (FIG. 1), the barbs 22 and the fins 14 alternate around the 
circumference of the top, the fins in the area of the barbs 22 being of 
lesser diameter than the barbs so that the barbs control the force 
required to effect the "on" action. Purposely the fins are not aligned 
radially with the barbs so that they do not stiffen or otherwise affect 
action of the barbs 22. 
Between the fins 14 (FIG. 3) the base flange 12 is formed with four 
quarter-circle openings 26. These are openings left by the core pin in the 
molding of the fastener. As will be noted from FIG. 5, ample space is 
provided as at 28 between the barb 22 and the fins 14. 
Turning now to the socket, as shown best in FIG. 4, it is generally 
designated 30 and comprises an annular base flange 32 having a cylindrical 
opening 34 centrally disposed. A sleeve 36 extends downward from the 
flange 32 and is integral with the flange about the opening 34, and the 
sleeve presents a mouth 38 which is tapered inwardly to a throat 40 inside 
the sleeve. A shoulder 42 is formed in the tapered mouth 38 for purposes 
which will appear. Above the throat 40 the socket is formed with a 
downwardly and outwardly slanting annular-bearing surface 44. Preferably, 
this surface is at an angle of about 15.degree. down from the horizontal. 
FIG. 6 shows in use a snap fastener embodying the invention. It comprises 
the socket 30 and the stud head 10 installed on plastic stripping S and S' 
respectively, which may be of plastic and having a thickness in a range of 
0.01-0.03 inches. 
In the setting operation the end of the mouth of the socket is curled over 
as at 46 to hold the strap S between it and the flange 32 so that the 
strap does not escape. The opening in the strap S is of smaller diameter 
than the curled-over edge 46. 
The stud head strap S' is also apertured, but with a smaller aperture, 
prior to the setting operation. In the setting operation a circular 
skiving tool comes down and from the chamfer of each fin 14 turns outward 
a curl 48 of plastic to clamp the strap S' between the curl 48 and the 
flange 12 so that there is no chance that prior to assembly the strap S' 
will separate from the stud head. 
In installation the end 20 of the stud head is introduced to the mouth 38 
of the socket and is pushed upwardly past the shoulder 42 and through the 
throat 40, the barbs 22 flexing inwardly as necessary. Above the throat 40 
the barbs 22 spring outwardly, as shown in FIG. 6, and engage or 
substantially engage the sides of the opening 34 with which they have a 
common diameter. The nubs 18 nestle under and against the shoulder 42 and 
serve as stop means precluding the further movement of the stud head into 
the socket. In this position the outer edges of the fins 14 engage the 
throat 40 snugly, the resilience of the parts assuring lateral immobility 
of the stud relaive to the socket. 
Attempts to withdraw the stud head from the socket result in the butting of 
the ends 24 of the barbs 22 against the bearing surface 44. Because the 
bearing surface 44 slopes outwardly and downwardly, there is a tendency 
for the barbs to spread even farther and reduce even more the likelihood 
that the parts can be unsnapped. What will happen is that the distal ends 
24 will nestle into the crotch between the cylindrical opening 34 and the 
bearing surface 44 and stay stubbornly there. 
Dimensions of the socket and head are such that the top 20 of the head is 
at a level slightly below the top surface of the socket flange 32. This 
assures that the head will not protrude from the back of the socket flange 
and will not create an undesirable projection. 
It should be understood that while the invention is shown in but one form, 
there may be many modifications and variations. The invention, therefore, 
is of more general scope and may be defined by the following claim 
language.