Abstract: A centering of the fixed key is obtained by means of its support, a perfect locking of the support of the fixed key is obtained by a key wedge, a displacement of the mobile key is obtained by the assembly of the square shaped support, the mobile pin is fixed thereto and the fixed pin secured to the body and parallel to the mobile pin, a displacement is provided through three ball bearings, a first ball bearing being housed in the support and two ball bearings in the wall of the body, then two protecting caps are secured on the body for outerly protecting the two ends of the mobile pin.