Army Force Universal Scope Mount Base for Pistol with Low Rail
[AS4355]

Exactly what I wanted. I have this fitted on my M1911A1 GBB pistol which has a plastic under rail mount (also bought from Airsoft Club) and the clearance is good, the rear sight catches a bit but that's because I need to cut the rail to size (it hangs over the back of the gun at the moment). A great product at an unbeatable price, came well packaged. It takes my red dot sight perfectly. (also bought from Airsoft Club)