Nitro Fin Slide Lock Thumb Rest 2.1 - 2011 / STI / SV Infinity / MPA / Prodigy Slide Lock Thumb RestTHE BEST THUMB REST SLIDE STOP AVAILABLE. PLEASE READ: Check your current slide lock for pin size. Use caution test fitting it before test firing at the range. The Nitro Fin by design fits close inside the slide lock relief of the frame, some gun smith work may be required. The Pin size is 0. 1985 +0. 0005 0. 0005 Slide lock does lock the slide back manually, but does not automatically on the last round. (Top Level Gunsmith Feature) Machined out of