The head of the nut (41) engages in a recess (22) provided in the second part (20).

A predetermined breaking point may be, for example, a groove or milled recess, in particular a notch (25).

The head (31) of the screw (30) bears against a recess (12) provided in the first part (10).

The first side of the plate is adapted to mate with a recess defined in a mine roof.

A lower end surface of the lower balance weight is provided with a countersunk hole in which a lower end of a rivet is accommodated.

According to the invention, the upper part comprises means (81) for tilting the screw, said means located onthe edges of the firstrecess.

Said second gear wheel bears a guide pin (8) that engages with a cut-out section (14) in the carriage (9).

The washer (40) also has a central countersunk hole (410) on the surface of which the widened end (320) of the shank (32) of the rivet (30) rests.

A lower panel punch forms the center panel, panel wall and countersink of the shell during upstroke of the press.

A reamer guide system may include a reamer guide that is configured to guide a reamer to at least two bones that are to be reamed to form a countersink.

A radius RF, RF' of said countersink (3, 3') may have a point M, M', said point M, M' being a radial maximum with reference to the center axis (2.1, 2. 1').

The countersinking angle (α) of the conical surface (6) is smaller than the cone angle (β) of the rib shoulders (16).

The end pieces (1, 21) also have a curved countersink (17) at each low pressure port which increases the drainage from the manifold (11).

The head (31) of the rivet (30) bears against a countersunk hole (12) made in the first part (10), the washer (40) bearing against the second part (20).

The shank projects into the bore and the two threads mate such that, as the dog rotates, the agitator screws on to the dog and the tapered head mates with the countersink.