IMPROVEMENTS IN SCREW BOLTS AND NUTS
Year: 1871

page_text: LETTERS PATENT to Thomas English, of Dulwich, in the County of
Surrey, for the Invention of "IMPROVEMENTS IN SCREW BOLTS AND
NUTS."
Sealed the 6th February 1872, and dated the 28th November 1871.
PROVISIONAL SPECIFICATION left by the said Thomas English at the
Office of the Commissioners of Patents, with his Petition, on the
28th November 1871.
I, THOMAS ENGLISH, of Dulwich, in the County of Surrey, do hereby
declare the nature of the said Invention for "IMPROVEMENTS IN SCREW
BOLTS AND NUTS," to be as follows:-
My Invention has for its object to reduce the liability of screw bolts
with cylindrical shanks and sunk or "minus" threads to break in the
screw threads when subjected to a longitudinal tensile stress; and
consists in forming bolts with the depth of the screw thread gradually
diminished, or with the diameter of the bolt at the bottom of the screw
thread gradually increased towards the direction from which the tensile

page_text: stress is applied to the part in question of the bolt, until the diameter of
the bolt at the bottom of the thread is the same as in the shank, the
diameter of the bolt over the top of the thread however remaining the
same throughout in either case.
If the depth of the thread in the bolt is diminished the interior 5
diameter of the nut over the top of the thread is gradually increased so
as to fit the thread of the bolt; and if the diameter of the bolt at the
bottom of the thread is increased the top of the thread in the nut is cut
away so as in this case also to fit the bolt.
SPECIFICATION in pursuance of the conditions of the Letters Patent,
filed by the said Thomas English in the Great Seal Patent Office
on the 12th April 1872.
TO ALL TO WHOM THESE PRESENTS SHALL COME, I, THOMAS
ENGLISH, of Dulwich, in the County of Surrey, send greeting.
WHEREAS Her most Excellent Majesty Queen Victoria, by Her
Letters Patent, bearing date the Twenty-cigth day of November, in the
year of our Lord One thousand eight hundred and seventy-one, in the
thirty-fifth year of Her reign, did, for Herself, Her heirs and successors,
give and grant unto me, the said Thomas English, Her special licence
that I, the said Thomas English, my executors, administrators, and
assigns, or such others as I, the said Thomas English, my executors,
administrators, and assigns, should at any time agree with, and no
others, from time to time and at all times thereafter during the term
therein expressed, should and lawfully might make, use, exercise, and
vend, within the United Kingdom of Great Britain and Ireland, the
Channel Islands, and Isle of Man, an Invention for "IMPROVEMENTS IN
SCREW BOLTS AND NUTS," upon the condition (amongst others) that
I, the said Thomas English, my executors or administrators, by an
instrument in writing under my, or their, or one of their hands
and seals, should particularly describe and ascertain the nature of the
said Invention, and in what manner the same was to be performed,
and cause the same to be filed in the Great Seal Patent Office within
six calendar months next and immediately after the date of the said
Letters Patent.

page_text: NOW KNOW YE, that I, the said Thomas English, do hereby declare
the nature of the said Invention, and in what manner the same is to
be performed, to be particularly described and ascertained in and by
the following statement thereof, reference being had to the accom-
panying Sheet of Drawings and to the figures and letters marked
thereon, that is to say:-
My Invention has for its object to reduce the liability of screw bolts
with cylindrical shanks and sunk or "minus" threads to break in the
screw threads when subjected to a longitudinal tensile stress; and
consists in forming bolts with the depth of the screw thread gradually
diminished, or with the diameter of the bolt at the bottom of the screw
thread gradually increased towards the direction from which the tensile
stress is applied to the part in question of the bolt until the diameter of
the bolt at the bottom of the thread is the same as in the shank, the
diameter of the bolt over the top of the thread however remaining the
same throughout in either case.
If the depth of the thread in the bolt is diminished the interior
diameter of the nut over the top of the thread is gradually increased so
as to fit the thread of the bolt; and if the diameter of the bolt at the
bottom of the thread is increased, the top of the thread in the nut is cut
away so as in this case also to fit the bolt.
Figure 1 of the accompanying Sheet of Drawings shows the section of
the end of a screw bolt and its nut constructed according to one modi-
fication of my Invention. In this case the depth of the screw thread,
which is sunk into the cylindrical surface of the bolt A is gradually
diminished in the direction from the point a to the point b (that is, in
the direction towards the shank of the bolt), while the diameter of the
bolt measured across the top of the thread is uniform throughout, and
equal to the diameter of the shank. This diminution of the depth of
the thread is by preference continued until the thread dies out at the
point b.
The interior diameter of the nut B over the top of the thread is in a
corresponding manner gradually increased from the point a to the
point b, so that the nut can be screwed on to the bolt to such a point
that each portion of the thread of the nut will be engaged with the
corresponding portion of the thread of the bolt. The length of the
thread of diminished depth on the bolt, and that of the thread of

page_text: increased diameter in the nut, are by preference such as compared with
the length of that part of the thread from a to c in which the diameter
is uniform, that the holding power of the part of the nut which engages
with the thread of diminished depth shall bear the same proportion to
the holding power of the other part of the nut as the difference between
the sectional areas of the bolt at the shank and at the bottom of the
thread bears to the sectional area of the bolt at the bottom of the full
thread; or, in other words, the holding power of the uniform part of the
thread from c to a should be equivalent to the tensile strength of the
bolt at the bottom of the thread, and the holding power of the tapered 1
part of the thread from a to 6 should be equivalent to the tensile
strength of the annulus of the bolt cut away by the thread.
The tapered portion of the thread both in the bolt and in the nut is by
preference formed by being chased in a lathe, the chasing tool being
gradually withdrawn from and brought nearer the centre of the lathe as 1
required.
It is immaterial with regard to the object of this Invention whether
the thread of increasing diameter in the nut be cut to its full depth,
as shewn in Fig. 1, or only to a depth corresponding with the outside
diameter of the thread of the bolt, but on account of greater facility of 2
manufacture it is by preference cut to the full depth whenever the
thread of the nut is formed by being chased in the lathe.
Figure 2 shows a section of a screw bolt and nut constructed according
to another modification of my Invention. In this case the before-
mentioned object of my Invention is attained by so forming the bolt A 2
that the bottom of the screw thread is gradually filled up, or the
diameter of the bolt at the bottom of the thread is gradually increased
from the point a to the point b, whilst the diameter of the bolt measured
across the top of the thread remains uniform throughout, such filling up
of the thread being by preference continued until the thread disappears 3
at the point b.
The top of the thread in the nut B is removed in such a manner and
to such an extent from the point a towards the point 6 as to correspond
exactly with the gradually increasing diameter of the bolt at the bottom
of the thread, so that, as in the previous case, the nut can be screwed 3

page_text: on to the bolt to such a point that each portion of the thread of the nut
will be engaged with the corresponding portion of the thread on the
bolt. The length of the thread which is gradually filled up on the
bolt, and of the thread in the nut which is gradually cut away,
is by
preference proportioned to the length of the thread of uniform diameter
from a to c, in the same manner as described with reference to Figure 1,
that is to say, the holding power of the threads from c to a is equivalent
to the tensile strength of the bolt at its weakest part; and the holding
power of the threads from a to 6 is equivalent to the tensile strength of
the annulus of the bolt cut away by the deepest thread. In this case
the thread of the bolt is by preference formed by means of a die or dies,
and the thread in the nut is formed of uniform diameter throughout at
its bottom, the tops of the threads in the nut being removed either before
or after cutting the screw thread therein.
The constructions above described are applicable to screw threads of
any pitch or section, but are of greatest advantage when applied to deep
threads. Also the proportions of the uniform to the tapering parts may
be varied, the best results however being attained when these pro-
portions are made as above described, and when the nut is screwed on
to the bolt as far as it will go, though some advantage will still be
attained from this construction even when the nut is not screwed up to
its full extent. When the nut is not screwed on so far as to engage the
taper threads, the bolt and nut are equivalent to an ordinary bolt and
nut, and may be used for all purposes to which ordinary bolts and nuts
are applied.
It may readily be understood that the tapering of the thread may be
effected by a combination of the two methods shown in Figs. 1 and 2,
that is to say, partly by the dying out of the thread of the bolt, as
shewn in Fig. 1, and partly by filling up the thread of the bolt, as
shewn in Fig. 2.
It may also be understood that instead of using one nut, as above
described, two shorter nuts might be employed, one behind the other,
and in this case the one nut may fit the uniform part of the thread of
the bolt from c to a, while the other is fitted to the part from a to b.
Having thus described the nature of my Invention, and in what
manner the same is to be performed, I would have it understood that I

page_text: do not claim the use of bolts so tapered that the diameter measured over
the tops of the threads varies while the depth of the thread remains
uniform, but I claim the use of bolts and nuts wherein the diameter of
the bolt measured at the bottom of its thread increases towards the
shank, substantially for the purpose and in the manner herein described.
In witness whereof, I, the said Thomas English, have hereunto set
my hand and seal, this Twelfth day of April, in the year of our
Lord One thousand eight hundred and seventy-two.
Witness,
CHA". D. ABEL,
20 Southampton Buildings.
THO. ENGLISH. (L.S.)