The Timney Trigger (Timney Model #511) consists of a left hand safety that blocks the trigger and not the sear. No screws, tapping, or drilling is required. Each trigger is geometrically identical with tolerances less than .0005?. The trigger is preset from the factory at 3 lbs and adjustable from 1.5 to 4 lbs. No gunsmithing required.
Note: The picture above illustrates a right hand model, however this product number is the left hand model.