Slip-joint pliers have a pair of plier members each having a jaw portion and a handle portion, a pivotal bolt, a nut, and a spring member. The spring member is arcuate and has long and short downward projections. One of the plier members has a bolt whole and an annular groove including a through hole for accommodating the spring member therein. The other plier member has a bolt hole defined by first and second slip changeover holes communicating with each other and an engaging recess contiguously communicating with the first slip changeover hole. The short downward projection of the spring member abuts the wall surface of the through hole and the long downward projection contacts the wall surface of either the first slip changeover hole or the engaging recess to automatically bias open the jaw portions of the pair of plier members.

FIELD OF THE INVENTION AND RELATED ART STATEMENT 
The present invention relates to slip-joint pliers provided integrally with 
a mechanism for automatically opening the jaw portions thereof. 
Pliers, one type of hand tools, comprises a pair of plier members each 
having a jaw portion and a handle portion and being attached pivotally to 
each other with a bolt and a nut so that the jaw portions of the plier 
members can be opened and closed relative to each other. There have 
heretofore been proposed such hand tools as pliers having mechanisms for 
automatically biasing the jaw or nose portions open for working 
convenience as in Japanese Utility Model Public Disclosure No. 57-170959 
and Japanese Utility Model Public Disclosure No. 59-127562, for example. 
In the former, opposite ends of a twisted coil spring are fixed to 
respective handle portions of a hand tool at a position in the vicinity of 
a pivot portion of the hand tool to apply spring pressure to the handle 
portions, thereby ensuring the automatic jaw or nose portion opened state. 
The latter has an ordinary coil spring interposed between opposed handle 
portions of a hand tool in the vicinity of a pivot portion of the hand 
tool and guarantees the automatic jaw or nose portion opened state by 
utilization of the spring pressure. 
These mechanisms are advantageous in that the jaw or nose portions are 
automatically opened by a very simple construction. However, since the 
coil spring serving as a pressure source for opening the jaw or nose 
portions is interposed between the handle portions is exposed to the 
outside in either of the conventional mechanisms, it not only makes the 
hand tool look worse but also constitutes an obstacle when using the hand 
tool. What is worse, the coil spring exposed to the outside is liable to 
be damaged and to be deformed owing to accidental external forces in 
handling the hand tool and therefore has a possibility of failing to 
sufficiently fulfill its function to automatically open the jaw or nose 
portions. 
OBJECT AND SUMMARY OF THE INVENTION 
The main object of the present invention is to provide slip-joint pliers 
provided integrally with a mechanism for automatically biasing the jaw 
portions thereof open at all times, which has a very simple construction 
and is capable of eliminating the aforementioned drawbacks. 
To attain the object described above, according to the present invention, 
there is provided slip-joint pliers which comprise a pair of plier members 
each having a jaw portion and a handle portion, a pivotal bolt having a 
rectangular shank, one of the pair of plier members having formed therein 
a bolt hole of a shape substantially the same as that of the rectangular 
shank of the pivotal bolt, the other one of the pair of plier members 
having a portion thereof corresponding to the portion of the bolt hole in 
the one plier member and comprising a bolt hole having first and second 
slip changeover holes communicating with each other for permitting 
adjustment of the opening angle of the jaw portions of the pair of plier 
members with respect to one another, a spring member formed in a ring 
shape with a gap and provided on one end thereof with a long downward 
projection and on the other end thereof with a short downward projection, 
the one plier member having an annular groove in the outer surface thereof 
about the bolt hole for accommodating therein the spring member and also 
having a through hole formed through part of the bottom of the annular 
groove so as to have a length substantially the same as a distance between 
the long downward projection and the short downward projection, the short 
downward projection being stopped by the wall surface of the through hole 
without projecting downwardly from the through hole and the long downward 
projection projecting downwardly from the through hole when the ring 
member has been accommodated within the annular groove, the other plier 
member having an engaging groove formed in the inner surface thereof 
contiguous to the first slip changeover hole which defines the bolt hole 
in the other plier member in conjunction with the second slip changeover 
hole, the long downward projection of the spring member projecting from 
the through hole in the one plier member being brought into contact with 
the wall surface of either the first slip changeover hole or the engaging 
groove, and a nut for holding the pivotal bolt in place therewith. 
The above and other objects, characteristic features and advantages of the 
present invention will become apparent to those skilled in the art as the 
disclosure is made in the following description of a preferred embodiment 
of the invention, as illustrated by the accompanying drawings.

DESCRIPTION OF THE PREFERRED EMBODIMENT 
The present invention will now be described in detail with reference to the 
illustrated embodiment. As illustrated in FIG. 1, the slip-joint pliers 
according to the present invention comprise a pair of plier members 1A and 
1B having jaw portions 2a and 2b and handle portions 3a and 3b, 
respectively. The plier member 1A has a bolt hole 4 of a shape 
substantially the same as the shape of a rectangular shank 6a of a pivotal 
bolt 6. The other plier member 1B has in a portion corresponding to the 
portion of the bolt hole 4 in the one plier member 1A a bolt hole 5 
composed of first and second slip changeover holes 5a and 5b for adjusting 
the opening angle of the jaw portions 2a and 2b in two stages. The two 
plier members 1A and 1B are pivotally attached to each other into 
slip-joint pliers by passing the pivotal bolt 6 through the two bolt holes 
4 and 5, holding the pivotal bolt 6 in place with a nut 7 and calking the 
leading end of the pivotal bolt 6 projecting from the nut 7, with the 
result that the jaw portions 2a and 2b are capable of being close to and 
apart from each other. The slip-joint pliers of the present invention and 
ordinarily known slip-joint pliers are common with each other in regard to 
the aforementioned aspects. 
The present embodiment, however, further comprises a spring member 11 
serving as a pressure source for opening the jaw portions 2a and 2b. 
Further, in this embodiment, the outer surface of the one plier member 1A 
has a circular recess 8 formed about the bolt hole 4 and communicating 
with the bolt hole 4 and also has a through hole 9 formed through part of 
the bottom of the annular groove 8 toward the inner surface of the one 
plier member 1A. The spring member 11 is completely accommodated within 
the circular recess 8 including the through hole 9 so as not to project 
upwardly from the annular groove 8. Further, the inner surface of the 
other plier member 1B has an engaging recess 10 formed therein so as to 
contiguously communicate with the first slip changeover hole 5a which 
defines the bolt hole 5 in the other plier member 1B in conjunction with 
the second slip changeover hole 5b and which sets the opening angle of the 
jaw portions 2a and 2b larger when it admits the shank 6a of the pivotal 
bolt 6. Denoted by reference numeral 12 in FIG. 1 is a washer interposed 
between the head of the pivotal bolt 6 and the spring member 11. 
To be specific, the spring member 11 is made from a resilient rod or plate 
material and is formed in the shape of a ring with a gap so as to have one 
end integral with a long downward projection 11a which projects from the 
through hole 9 toward the side of the other plier member 1B and contacts 
the wall surface of either the first slip changeover hole 5a or the 
engaging recess 10 when the spring member 11 has been accommodated 
completely within the circular recess 8 and to also have on other end 
provided integrally with a short downward projection 11b which is engaged 
with the wall surface of the through hole 9 without projecting downwardly 
from the through hole 9 in the state of the spring member 11 having 
completely been accommodated within the circular recess 8. The distance 
between the long and short downward projections 11a and 11b across the gap 
of the spring member 11 is substantially identical with the length of the 
through hole 9 in the one plier member 1A. 
The pair of plier members 1A and 1B are assembled into slip-joint pliers by 
completely accommodating the spring member 11 within the circular recess 8 
with the long and short downward projections 11a and 11b inserted into the 
through hole 9, inserting the washer 12 into the through hole 9 on the 
spring member 11 as the occasion demands, then passing the pivotal bolt 6 
through the bolt holes 4 and 5, subsequently holding the pivotal bolt 6 in 
place with the nut 7, and finally calking the leading end of the pivotal 
bolt 6 projecting from the nut 7. The slip-joint pliers of the present 
invention thus assembled is nearly identical in appearance with 
conventional slip-joint pliers not having a mechanism for automatically 
opening the jaw portions, as illustrated in FIG. 2, and is used similarly 
to the conventional slip-joint pliers in the state of the jaw portions 2a 
and 2b being set at one of the two adjustable opening angles determined by 
the engagement of the shank 6a of the pivotal bolt 6 in the first and 
second slip changeover holes 5a and 5b defining the bolt hole 5 in the 
other plier member 1B. 
In the slip-joint pliers of the present invention, however, when the shank 
6a of the pivotal bolt 6 is engaged in the first slip changeover hole 5a 
for making the opening angle of the jaw portions 2a and 2b larger, the 
short downward projection 11b of the spring member 11 contacts the wall 
surface of the through hole 9 and, as shown in FIGS. 3A and 3B, the 
leading end of the long downward projection 11a projecting downwardly from 
the through hole 9 contacts the wall surface of the engaging groove 10 
contiguously communicating with the first slip changeover hole 5a to apply 
the spring pressure produced by the long downward projection 11a to the 
other plier member 1B, thereby biasing the handle portion 3b of the other 
plier member 1B from the handle portion 3a of the one plier member 1A and 
thus causing an automatic opened state of the jaw portions 2a and 2b. On 
the other hand, when the shank 6a of the pivotal bolt 6 is moved to and 
engaged in the second slip changeover hole 5b for making the opening angle 
of the jaw portions 2a and 2b smaller, as illustrated in FIGS. 4A and 4B, 
the long downward projection 11a of the spring member 11 moves from the 
engaging groove 10 to the first slip changeover hole 5a and contacts the 
wall surface of the first slip changeover hole 5a to apply the spring 
pressure produced by the long downward projection 11a to the other plier 
member 1B, thereby biasing the handle portion 3b of the other plier member 
1B from the handle portion 3a of the one plier member 1A and thus causing 
the automatic opened state of the jaw portions 2a and 2b. In either case, 
when the handle portions 3a and 3b are grasped when using the slipjoint 
pliers, the long downward projection 11a of the spring member 11 is 
pressed against the wall surface of either the engaging recess 10 or the 
first slip changeover hole 5a to be flexed toward the short downward 
projection 11b within the through hole 9 due to its resiliency, thereby 
allowing the handle portions 3a and 3b to move close to each other. 
Therefore, the slip-joint pliers of the present invention can be used 
without hindrance. As soon as the grasp is released, the spring pressure 
of the long downward projection 11a of the spring member 11 acts on the 
other plier member 1B to automatically the jaw portions 2a and 2b. 
As described above, according to the present invention, since the spring 
member serving as a pressure source for automatically opening the jaw 
portions of the pair of plier members is completely accommodated within 
the annular groove formed about the bolt hole in one of the plier members, 
it is not exposed to the outside and therefore not only makes the 
slip-joint pliers look better as compared with the related art cited 
herein but also solves the problems of an obstacle in the use of the 
slip-joint pliers and damage or deformation owing to accidental external 
forces which have been posed by the spring members of the related art. 
Further, since the small downward projection of the spring member contacts 
the wall surface of the through hole in one of the plier members whereas 
the long downward projection of the spring member contacts the wall 
surface of the engaging groove in the other plier member when the shank of 
the pivotal bolt is engaged in one of the two slip changeover holes 
constituting the bolt hole in the other plier member and with the wall 
surface of the one slip changeover hole when the shank of the pivotal bolt 
is engaged in the other slip changeover hole, pressure produced by the 
long downward projection is exerted on the other plier member in either of 
the two states and, therefore, the automatic opening of the jaw portions 
of the pair of plier members can precisely be ensured.