The Speed Screw replaces the rear leg in the Sinclair Rifle Rest. It is used for high speed vertical travel between the record target and the sighter target, and for quick fine-tune vertical adjustments. All stainless steel construction and quality machining make this product work flawlessly. NOTE: 3/8"-16 thread Speed Screw works with Gen II Sinclair rests, Hart, Bald Eagle and others with 3/8"-16 leg threads. 1/2"-20 thread Speed Screw works for the new Sinclair Heavy Varmint Rests and Sinclair Competition Rests. Mfg: Sinclair International