Mastercool low-Side Manual Coupler features patented manual couplers that adjust easily to R-134A service ports with varying dimensions. It is made of an all metal construction for extra durability and the patented, spring loaded depressor prevents damage of service valves. The coupler can be removed from service ports regardless of knob position without losing refrigerant. It convenes SAE, UL and EPA recommendations for containment of refrigerant..