Grease can be pumped into a grease fitting by using a grease gun coupler, which joins a grease gun hose or extension to the fitting. The male threaded connection on the hose or extension matches the female threaded connection on a grease gun coupler. A mechanism on the other end of the coupler either snaps or locks onto the grease-fitting head to secure it. The coupler is equipped with internal jaws that seal the fitting and stop grease leaks.