A frame lug for a firearm having a receiver or barrel hingedly mounted to a frame is provided with a tension post having an external thread that adjustably engages with an internal thread of a vertical bore in the frame lug. The tension post provides a height adjustable top surface upon which the receiver or barrel rests when in a closed position and maintains a tight metal-to-metal connection to improve precision of fitting together the receiver or barrel and the frame. Firearms may have the frame lug installed therein or be retro-fitted with the frame lug. In a retro-fitting method, the firearm's frame lug is removed, a threaded vertical bore is machined at least partially into the frame lug, and an externally threaded tension post is adjustably engaged with the vertical bore such that a top surface of the tension post provides a tight fit with the receiver or barrel.