I purchased these 1/4" Male Flare to R-134a Access Port Adapters for My Husband!He had several different sets of these, and had loaned them to friends, and never got them back! So I purchased these for him, and he said they were the best "Quick Connect" access port Couplers He's ever Used!The Knurling on the release lock is easy to grip and release with one hand without slipping, and the seal off after removal was excellent. No spent refrigerant loss!He's a Retired Refrigeration Mechanic...so I trust his liking of this coupler set!.....And these are a MUST for accessing the service ports on automotive a/c systems with the R-134a refrigerant!....Great Product!