PIPE WRENCH WITH DIFFERENTIATED TOOTH SIZE Background A pipe wrench consists of two shanks with toothed jaws, each jaw at at angle of 45-90 degrees from the rest of the shank. The shanks are connected at a joint, and the joint is fixed relative to the inner jaw, while the outer jaw and its shank can be translated relative to the joint to adjust the gap between the jaws to fit the diameter of the actual pipe or tube to be gripped. The teeth of the jaws serve to give enough friction against the pipe even if there is a surface layer of low strength, such as paint or plastic coating.

The invention concerns an improved type of teeth, better adopted to pipes of varying diameter with less risk of the jaws slipping against the pipe surface with resulting damage.

Description Pipe wrenches according to the invention are described with reference to the figures 1 and 2, showing two types of wrenches with teeth according to the invention, figure 1 an American type with one long and one short shank, figure 2 an European type with two long shanks. Figure 3 shows in detail the jaws gripping a pipe with large diameter, figure 4 the jaws gripping a smaller diameter pipe.

When a pipe wrench grips a pipe (10), the outer jaw (11) and the inner jaw (1 2) are pressed against the pipe with basically the same radial force, while the tangential force is larger at the inner jaw than at the outer, depending on the different angles from the joint (13) where the shanks (14,15) meet, to the contact points at the jaws. When trying to rotate the pipe, a force is applied to the shank (14) of the inner jaw, and the inner jaw will normally slip before the outer jaw. The pipe will then roll against the outer jaw until it touches the inside (16) of the shank (15) of the outer jaw. For each pipe diameter there will finally be one characteristic contact point on each jaw. A pipe with large diameter (30) will have final contact with teeth (31,32) at a large distance from the inside (16), and

a smaller diameter pipe (40) will have final contact with teeth (41,42) at smaller distance from the inside.

The jaws have teeth in order to penetrate surface layers on the pipe to get a secure grip.

The teeth should preferably be unsymmetric and leaning in the direction the pipe is to be turned. The size, sharpness and pitch of the teeth should be such that two or three teeth touch the pipe at each jaw contact. A single tooth contact is unstable, with indeterminate angle, and a four teeth contact will not securely penetrate the surface layers. Pipe wrenches according to known technique have teeth of equal size, and their size and pitch are compromizes between what is optimal for different diameters.

According to the invention, the teeth should have different sizes adjusted to the diameter of that pipe which will touch the teeth and the inside (16) at the same time. Accordinly, teeth (41,42) near the inside (16) should be small and close, the teeth far from the inside should be large with greater distances. The largest teeth should have height and distance at least 25 % larger than the smallest, preferably 35-40 % larger. The tooth size could be varied continously or in steps.

the teeth should preferably be made unsymmetric in known manner by making the leading tooth flank leaning 65 degrees and the trailing flank 45 degrees from the plane of the jaw. The tooth tips should be at the same level to facilitate gripping of polygonal bodies like nuts or bolt heads.

The invention is not limited to wrenches where a threaded nut is used to adjust the gap between the jaws,as shown in figures 1-2, but can be applied to all wrenches where two jaws can be located at different distance to grip and hold various sizes of pipes, tubes, shafts, bars and other round items.