Abstract: A mechanical device converting rotary input to linear compression or stretching output with a high mechanical advantage and with a minimum of frictional losses which comprises a screw member having multiple lead threads and a pair of jaw assemblies carried on the screw member. Each of the jaw assemblies comprises a plurality of roller members equal in number to the thread-starts on the screw member and an outer member having internal annular grooves in rolling contact with the roller members. The roller members of one of the jaw assemblies have a larger pitch-diameter than the pitch-diameter of the rollers members of the other jaw assembly.