Steel tube prop with rapid release

Claim 1

A prop-type support, comprising: (a) telescopically interengaging inner and outer tubes; (b) an external screw thread on said outer tube; (c) an axially elongated slot traversing the outer tube in the region of the screw thread; (d) a series of axially spaced holes traversing the inner tube; (e) an internally screw threaded sleeve, the sleeve being received on the screw thread; and (f) a support pin traversing the slot and a selected one of the holes, the support pin having a longitudinal axis, the sleeve bearing against the pin to maintain the tubes in a required relative spacing against an end load, the pin including first and second engaging surfaces for engaging a wall of the inner tube, each of the engaging surfaces being, at a first radial spacing and a second, different radial spacing, respectively, from the longitudinal axis of the support pin, such that a the pin being in a first position with the inner tube bearing against the first engaging surface which is at a greater radial spacing from the longitudinal axis of the pin than is the second engaging surface, rapidly lowered by an amount equal to the difference between the first radial spacing and the second radial spacing of the first and second engaging surfaces of the support pin. of substantial axial extend so as to serve as a bearing surface and being