At last, the one screw on the Theoben Rapid you can't do without. These have to be made from scratch as it's a fine threaded metric M7 that don't exist with an obsolete 2BA British tread inside. Just to top it off, it then has to have a hex socket milled in the top. Made from silver steel for hardness.
PLEASE NOTE!! This is a location screw to align the transfer port correctly and mount the scope. Do not overtighten, the barrel is held in place by the forward clamp.