BSA Unit Twins Petrol Gas Tank Mounting Bolt. Bolts Measure 5/16″ X 5/8″ with a Thread Pitch of 22 (BSF) – Fits BSA Unit Twins (Lightning, Royal Star, (Firebird Scrambler Up To 1969), Rocket, Thunderbolt, Spitfire, Etc) from approx 1967-1970 with the “American” Small Steel & Fiberglass Tanks. Also fits many BSA “Light Weight” Models (C10, C11, D10, Etc) ! Please refer to your parts catalog for proper fitment.Please note that this bolt is sold each as picturedMade in EnglandO.E.M Part number 21-5662, 21-6050, 02-0923 or 60-2330