The LockNLube Grease Coupler XL is compatible with all grease guns and Zerk fittings. It does not leak once locked on and will not pop off under pressure. No hands are needed to align or hold the coupler in place while greasing. You have both hands free to operate your grease gun and know that the grease will go in, not on, your machine. Guaranteed. The XL is suited for all machines, but especially useful for U-Joints, Harvester Heads, shielded PTO shafts, and any fittings buried deep behind a shield. With almost 4? of reach, you can be confident that youll reach your fittings and grease will go in, not on, your machine. When you want to release the coupler, simply depress the thumb lever, even at extreme pressures. Watch the video on this page for a demonstration. PRODUCT FEATURES It has a unique sliding sleeve, activated by a thumb lever. The sleeve locks the four spring-steel jaws onto the Zerk fitting, and releases the jaws by pushing on the thumb lever. When the jaws are locked onto the Zerk, a leak-proof seal is created. The locked connection is positive and rigid preventing the coupler from coming loose and breaking the leak-proof seal. If a fitting becomes pressurized, especially a recessed one, just depress the thumb lever and release the coupler. REPLACEABLE SEAL & JAWS The LockNLube Grease Coupler XL is fully rebuildable. If it starts to leak, you simply replace the seal and jaws and it is as good as new. See our tutorial here. We include a free replacement seal and jaws with every coupler that we sell. Additional Seal Kits are also available from our store. The seal kits for the LockNLube Grease Coupler and the LockNLube Grease Coupler XL are identical and can be used in either model.