The threads (17) of the upper shaft may be configured in an inverted buttress design.

The spindle (9) has a trapezoidal thread (8).

There are more than 100 different types of thread, from ACME, an American trapezoidal thread, to Yv, a Turkish round thread.

The bolt dimensions are M 138 with a modified trapezoidal thread.

A traditional screw essentially consists of a steel shaft with trapezoidal thread and a bronze, metal or plastic nut.

The spindle (9) having the trapezoidal thread (8) is supported by supporting means (31) on the area opposite the threaded part (7a), and said means can be attached to the frame (2).