Precision needle punch valve, designed to work with 1/4", 5/16" and 3/8" O.D. sizes; used to recharge refrigerant gas. This valve is composed of several screws and an Allen wrench. This Allen wrench helps to make the perforation where the gas will be recharged when connecting the hose. Once this process is finished, the valve is closed with the same Allen wrench, leaving the copper tube completely sealed. This is exactly why this method of refrigerant gas recharge is single use.