its for m18 threads i need to know what size o ring this is on unit please who ever replys dont tell me 40 difrent sizes i need this size that fits the m18 threads i used little to large of a o rings when fill my gun with m18x1.5 threads sticking out filled little over 200bar and the over sized o ring blowed out i took o ring off a reg like in pict i did not mesure it but was smaller and worked perccfect held 300 bar no leaks 
