Shear screw
A shear screw has predetermined breaking points in two planes, separated axially from one another, and it has centrally a blind hole extending over a substantial length and having a cross section which is suitable for transmitting a torque to the shear screw by means of a pin-like tool of adapted dimensions which can be inserted into the blind hole. The blind hole extends to about level with the predetermined breaking point which is arranged in the lower region, facing the end face of the shear screw, of the latter and has a strength greater than that of the other predetermined breaking point.
1. Shear screw for fastening an electrical conductor in a metallic terminal shaped as a tubular piece, with at least one through-hole in its wall provided with a thread, for receiving said shear screw, said shear screw comprising:
a head;
a threaded part;
a first predetermined breaking point;
a second predetermined breaking point, wherein said first and second predetermined breaking points are separated axially from one another with said second predetermined breaking point having a greater strength than said first predetermined breaking point; and
a centrally arranged blind hole extending over a substantial length through said shear screw having a cross section for accepting a pin like tool having a corresponding cross section for transmitting a torque to said shear screw wherein
said blind hole extends to about level with said second predetermined breaking point which is arranged in a lower end face region, of said threaded part of said shear screw, and wherein
said shear screw has formed in it, concentrically to said blind hole, a recess, axially shorter than said blind hole and having a cross section identical to the cross section of said blind hole, and is displaced with respect to said blind hole in the circumferential direction at an angle lying preferably between 10° and 40°, and which recess extends to about level with said first predetermined breaking point which is arranged in an upper region between said head and said threaded part of said shear screw, and wherein
an orifice of said blind hole and said recess at said head of said shear screw is dimensioned in such a way that said pin-like tool can be inserted only into said recess and not into said full depth of said blind hole.
2. Shear screw according to claim 1 , wherein the blind hole, recess and tool have a polygonal cross section.
3. Shear screw according to claim 2 , wherein the cross section of blind hole, recess and tool is a hexagon.
4. Shear screw according to claim 1 , wherein the predetermined breaking points run at right angles to the axis of the shear screw and parallel to one another.
5. Shear screw according to claim 1 , wherein the predetermined breaking points run obliquely to the axis of the shear screw.
6. Shear screw according to claim 5 , wherein the predetermined breaking points run towards one another in opposite directions so as to form an acute angle.