there is six locking balls in the coupler which hold the plug securely, Push-on style coupler, insert plug into coupler for fully automatic, quick coupling action without pulling sleeve back. Color matching system dedicated line use - ensures you never use a lubricated line for dry line applications, preventing cross contamination. High quality rubber shock absorbers can better protect the skin and increase friction. the quick connect system needs just a simple push to connect couplers with plugs. this kit can be widely used on different air tools such as air compressors, air blow guns, air nailers etc,it is of top quality for daily use and can meet needs of heavy users.