FOR TWIST AND LOC GAS TANK USED 1936 UPTO 1988 THIS IS A DEEPER NECK NON VENTED CAP, IF YOU LOOK INSIDE YOUR TANK YOU WILL NOTICE ONE NECK IS DEEPER THAN THE OTHER, THIS IS THE DEEPER ONE, STOP FUEL LEAKING OUT ON THE SIDE STAND, WORST WAY YOU CAN ALWAYS USE A EXTRA RUBBER TO PACK IT OUT TIGHT