The DiversiTech VCC-4B refrigerant locking caps by COP-CAP are an effective way to discourage and prevent the removal of refrigerant. They fit the standard service valve on all central AC units and mini-splits. The caps can only be removed with the included special tool. Simply thread the cap assembly onto existing 1/4 in. flare connection on system and lock set screw in place with hex wrench provided.