Vintage British motorcycles such as Triumph, BSA and Norton use fuel valves with 1/4 inch BSP (British Standard Parallel) threads. These reproduction petcocks feature all metal internals and a cleanable fuel filter. This will replace the leaky, hard to turn, worn out petcock on your vintage motorcycle and give you trouble-free performance. OEM part number is 83-2801, and was found on most Triumph 250, 500, 650 and 750 cc singles twins and triples from the 1950's through the early 1980's. On the majority of British bikes this valve works on they will have a reserve valve on the left side of the tank and the main valve on the right side . Then the carb or carbs would have a dual banjo fitting so they are connected together at the bottom for a dual carb application or a dual banjo on a single carb . Then only the right valve is used until the reserve is needed and then you turn the left on to get the rest of the gas out of the tank . There will not be 3 positions on this style valve it is either ON or OFF.