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Патент USA US3079978

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.Ma_rch 5, 1963
Filed Aug. 26, 1959
(514.16% EQ/rao-QFM
United tates Fatent
Patented Mar. 5, 1963‘
FIGURE 8 is a view in cross-section taken on line 8—8
Filed Aug. 26, 1959, Eel‘. No. 836,108
7 (Ilaims. (El. 151-—7)
of FIGURE 1; and
FIGURE 9 is a view in cross-section taken on line 9-9
of FIGURE 2.
Referring to the drawing, FIGURE 1 discloses a tapered
self-tapping screw 2 having a sharp point or tip 4 and an
elongated cylindrical shank portion 6 adjacent the head 8
of the screw. A portion 10 of the shank adjacent to the
tip of the screw 4 is greater in diameter than the shank
This invention relates to improvements in self-tapping 10 portion 6. Threads 12 which extend around the shank
portion of enlarged diameter also have somewhat greater
sheet metal screws and relates more particularly to self
root and crest diameters than elsewhere along the shank.
tapping sheet metal screws which are also self-locking.
The illustrated shank and thread portions of enlarged
Machine screws, bolts, and the like have been rendered
diameter are shown in exaggerated fashion in the draw—
self-locking by providing them with resilient inserts as
ings for the purpose of description, but in actuality the
disclosed in the Brutus US. Patent No. 2,520,121 and the
increase in diameter over shank portion 6 and thread por
Boots Patent No. 2,539,887. The resilient inserts provide
tion 14- adjacent screw head 8 is preferably less than .005
a locking action by forcing together the threads of the
mating threaded elements at the opposite sides thereof
Located in the upper shank portion 6 is a radial cylin
from the insert. Attempts have been made to use such in
drical hole 16 (FIGS. 1 and 8), in which is mounted a
serts in self-tapping sheet metal screws but these attempts
resilient locking plug 18, formed of “nylon” or its equiva
have failed for the reason that when the screw is driven
lent. The insert 18 is of such length with respect to the
into the sheet metal the outer portion of the insert invari
hole, that its outer end projects beyond the root line of
ably is sheared off or damaged to the extent that its lock
the threads and may extend ?ush with or slightly beyond
ing action is destroyed. Damage occurs to the insert even
the crest of the threads 12 adjacent thereto. As explained
when an expansion space is provided in the insert-receiv
above, the plug is deformed when the screw is driven into
ing recess of the screw as shown, for example, in the
a hole or an upset portion around a hole in a sheet of
Brutus U.S. Patent No. 2,520,121.
metal and due to its resiliency reacts to urge the screw
Study of the difficulty encountered with the use of
sideways into increased cohesive frictional engagement
resilient inserts in self-tapping screws leads to the con
with the metal diametrically spaced from the insert or
clusion that the zero clearance between the sheet metal
and the screw driven into the hole causes the projecting
When the screw is driven into a drilled or punched hole
portion of the insert to be abraded or sheared away as
in a piece of metal which may or may not be upset to
the screw was driven into the metal. As a result, the part
provide additional thickness, the thicker portion 10 of the
of the insert, if any, left projecting beyond the roots of
shank and threads of greater crest diameter slightly en
the threads of the screw is of insu?icient size to produce
large the hole in the metal to provide a slight clearance
the reaction e?ect required to lock the screw in the metal.
between the shank portion 6 of the screw and the side of
In accordance with the present invention, self-tapping
the hole and to enable the resilient insert to be deformed
screws are provided which, as they are driven into the
between the screw threads, screw shank and the side of the
sheet metal, tap threads therein and a clearance for the
hole without abrading or shearing off the projecting por
resilient insert su?icient to prevent the portion of the in
tion of the insert. The .005 inch diameter clearance, or
sert extending beyond the roots of the screw threads from
.0025 inch radius clearance or less is insufficient to result
being sheared or abraded away.
in a “loose ?t” of the screw and the resiliency of the in
More particularly, the new screws have enlarged por
sert and its reaction force securely locks and retains the
tions between the tips or points of the screws and the
screw against rotation in the metal.
resilient inserts therein to render the hole into which the
FIGURE 2 is a modi?cation of the invention in which
screw is threaded slightly oversize and thereby provide
the self-tapping screw has a threaded shank provided with
the necessary clearance enabling the projecting portion of
a tip 4-’, a shank portion 6’ of generally uniform diameter
the insert to be deformed and compressed, without shear
adjacent head 8', a thickened portion 10', and threads 12'
ing or abrasion, between the screw and the wall of the
conforming to the shank 10’ as described above. The
mating hole, and without however producing a loose ?t
shank contains a rectangular slot or recess 20 (FIGURES
of the screw in the hole.
2 and 9) for receiving a strip 22 of resilient material
The insert may be in the form of a cylindrical plug, a
such as “nylon” or its equivalent. The slot 20 may be
rectangular or tapered strip, or the like, seated in a slot
formed by a milling operation with a circular cutter to
of general complementary shape.
form concavely curved bottom portions 24 in the recess
For a better understanding of the invention, reference
at the ends thereof. The strip 22 may be shaped to be
may be had to the accompanying drawings, in which—
press ?tted in the slot but is somewhat shorter in length
FIGURE 1 is a side view of a typical self-tapping screw
than the slot to provide expansion areas 24 at each end
embodying the present invention;
of the slot formed by the milling cutter. As shown in
FIGURE 2 is a side view of an embodiment of the
FIGURE 9, the resilient insert extends about flush with
present invention, containing a modi?ed form of locking
or slightly above the crests of the threads 14'. In the area
where the threads 12’ are of greater crest diameter, the
FIGURE 3 is a side view of a modi?ed form of self
outer surface of the insert is slightly below the crest of
tapping screw utilizing the present invention;
the threads. When the screw is screwed into a hole in a
FIGURE 4 is a side view of another form of self
tapping screw according to the invention;
FIGURE 5 is a side view of still another form of the
piece of metal, some of the insert at the thickened portion
of the shank may be abraded or sheared away, but the
self-tapping screw;
part of the insert strip in the shank portion 6' will be
FIGURE 6 is a side elevational view of a self-tapping
screw utilizing a modi?ed form of locking element of
essentially intact and will provide the desired locking
the type shown in FIGURE 2;
FIGURE 7 is a side elevational view of a modi?ed self
tapping screw having a locking strip mounted thereon;
FIGURE 3 illustrates another type of self~tapping screw
having a ?at tip which is of a type used in sheet metal,
plastics and the like. This screw has threads 26 and a
substantially in excess of .005” greater in diameter than
the shank portion having said- recess and insert-1 member
shank‘ portion 28 of ‘greater diameter than the remainder
of the- threads, and. shank. of the screw. A; resilient insert
32 is located between the head of the screw and the en
larged portion of the shank.
3. A self-tapping screw as claimed in claim 1 wherein
“FIGURE 4f.'illustratesl'ai screw similar to the screw CI said recess is substantially cylindrical and extends radially
shown in FIGURE 3 except that the thread 341is- inter
of the screw shank, and said resilient insert member is
rupted to improve its tapping action.- 'The '?rst three
frictiona'lly engaged within said recess and has a‘ portion
threads are shown as interrupted so as to provide‘ a cut
extending substantially to the crests of the thread adja
surfatce 3810111 the third thread‘ which‘: is one of the
cent thereto.
threads of enlarged" diameter- The leadingend: of thread‘
4. A self-tapping screw as claimed in claim- 1 wherein
40 is double thread of reduced height. This enables the
said recess is a slot in and extending lengthwise of one
complementali threads: to be tapped‘ in thev sheet metal or
side of said screw’ shank and said resilient insert member
is substantially complemental to and ?ts Within said slot
with its? outer‘ edge extending beyond th’e'roots‘ of the
the: likerwith‘out undue; strain on‘. any one or' any portion
of the“ threads; of the screw:.
thread’ adjacent thereto:
FIGURE 5 isv a: modi?cation‘- of the‘ embodiment of
3 showing at longer screw having the‘ enlarged‘
or' thickened! portion of the’ shank. and‘ the‘ larger diameter
threads spaced‘ farther' from the free end' or tip‘ of- the
screw/than‘ in the screws‘ described above. The expansion‘
tovmaximumr diameter in they FIGURE‘ 5" embodiment is
more gradualgiresulting'in easier'driv-ingof the'screw‘int'o
the sheet metal.
5.v A-self-tapping screw as claimed‘ in‘ claim' 4' wherein
said slot- extends parallel to the axis of the: screw and
substantially.v the full length‘ thereof.
6'. A self-tapping screw as‘ claimediin‘ claim 4' wherein
said‘ slot comprises end portions- permitting- expansion of
saidr'esilient insert’ member.
' 'Ii'he screw/shown i?‘FIG'UR-E‘G istsimilar to thetscrew
7‘. A self-tapping sheet’ metal screw comprising a head;
a- shank ?xed'to said head‘ and having: an outer end2 of
shown‘. i111~ FIGURE 3‘ but having? therein av slot 44? and'
smaller diameter than‘ the remainder o?said shank‘ps'aidi
resilient locking-t strip‘ 46 similar to?- the locking’ strip'iil
shank having ar-?rst shank-‘portion adjacent said h‘eatl'fptir2
lust'ratedl in‘: FIGURE‘, 2'.’
tion‘» and1 a second shank portionbetweenl said-‘outer end
and‘ said ?rst shank portion‘,-a1r'e‘cess'- in‘ said’ shank exi-v
tending. into said ?rst shank portion; a resilient locking"?
insert inlsaidirecess, said second‘ shank portion being of
greater diameter than said‘ ?rst'nameds'hank portion; and‘
The“- screw: shown: in: FIGURE7 i‘sisimilar'to‘ithat shown '
in FIGURE; 6‘ with the‘ exception? that~ the threads‘ are in
terrupted as: at 48'.
Although. the" resilient, insertsi arev preferably made" of’ 0
nylon,‘ other.’ materials resilient‘: or‘ elastic in nature and
c'a‘pab'lef'of providing-a“ grippin'gvsurface with theimetal-or
oth'er‘composi'tion of the: female member can be utilized;
I claim:
a plurality of convolution's'of‘ a helical~ screw threadio'n
said shank, said- tliread' being" of substantiallyvv uniform
cross-section throughout‘ themajor portion of its length?
for tappingithreads'in sheet metal, said?thread'havingianl
1. A self-tapping, self-locking sheet metal screw com 35 axial root' dimension‘ at least as great as the axial base
prising; a; shank having: a: plurality‘ offc'o‘nvolu‘tions'v of? a
dimension of said thread,is'aid second named slia'nk‘rporl
helical screw thread: thereontfor' tapping; threads in: sheet
tion'havin'g' thread portions thereonl of slightly" enlarged
metal, said: thread being;off'substantially‘uniform cross;
section. throughout: the major: portion 0f'its1 length and
root and crest‘ diameters adapted to- form-haul enlarged
female’ socket thread‘ providing clearance- for expansion»
having an axial: rootl dimension; at: least as-Lgreat'! a's-th'ei 40 of said resilient‘ insert‘, s'aid'insert' extending radially! be;
axiallb'as‘e:dimensioniofi'th'e thread; said“ shankihavin'g 'a'tip'
yond the root line ofsaid‘thr'ead onls‘a'id ?rstshankiphr
smaller- tharn said‘ shank‘ and: a head: a‘ti the end- of said
shankt opposite said tip; . a portion - of said‘ shank: between'ry
References Gited-in’the ?le of this patent
saidih'ea'diandi tip having‘; threads of greater! root-diameter‘
thanithe-remainder'of sa'idi shank, a- recesslinith'e' side of 45
the‘ s'crew shank,- at=v leastI av part1 of- which‘ is positioned
between said? portion of greater‘ root diameter and said
head,’ and~a resilient‘insert-member, in‘saidirece'ss extend
. 192,636
Collins et all __________ _>__ July»
Ryan .; _______________ “June 17,1913‘
Kahn ________________ .._. Sept. 3, 1946
Lyon ___-_ ____________ __ Oct. 22, 1946
Brutus _______________ __ Aug. 29, 1950v
2; A‘ selfita'ppingiscrew as claimed'in claim 1', in‘which
said'sh'ank andlthread portionof greater diameter‘ are not
Bo'ots' _____ _-____- ______ __ Jan. 3'0,.1951~
Buckley.‘ ____________ __,__ June 25, .1957}
McKay et al..__'_ _______ __ Oct; 18,1960
ingradially beyond the root’: line, o'f‘sai'd" portion of said‘
thread b‘e'tweeri'said head'an'd ‘said’ enlarged ‘root diameter
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