In 1938, Colt released a .22-caliber conversion unit. With this kit, one who already owned a "Government Model" could simply switch the top half and fire inexpensive .22 rimfire ammunition. Unit consists of a slide marked "Service Model Ace" barrel, with floating chamber, ejector, slide lock, bushing, recoil spring, 10-shot magazine and box. Conversion Units feature the Stevens adjustable rear sight. Later that same year a kit to convert Service Model Ace to .45 ACP was offered. In 1942 production of these units ceased. The .22 kit was re-introduced in 1947; .45 kit was not brought back. Be alert, as sometimes a conversion unit is found on a Service Model ACE receiver and a Service model Ace upper is sold as a "Conversion Unit". Conversion Units are ALWAYS marked "Conversion Unit". "Service Model ACE" pistols lack the "Conversion Unit" marking. NOTE: Finish 99-100 percent add 20-30 percent. Deduct 20 percent if box is missing.