Alright thanks, I knew the purpose of it just couldn't coin the correct term. I'm probably just going to pick up a replacement in case need be I have it on hand. Another question I have completely unrelated is about my MacDev Carbon Fiber 68/4500. I recently got it rehydro tested and it passed but after airing it up the fill nipple leaked so I purchased a new one and when I put it on I didn't put a towel around it when tightening and ending up getting these scratches. Are they harmful to the reg/tank at all? And I have noticed the tank leaks some air when just being stored during the week. Could that be because I didn't use teflon tape on the reg when screwing into on the tank? Any input is helpful.