Original Item:  The Sten Return Spring Housing acts as a guide for the return (recoil) spring and prevents the kinking problems common to some submachine guns.  The button projecting from its rear surface retains the butt stock or the hand grip on the gun, being another fine example of the efficient engineering thought applied to the Sten.  Used.  British WW2 manufacture, interchangeable with all marks of the Sten gun.