Use in a standard AR lower to test trigger without risking damage to the lower. The one pictured has been tested in four lowers (with different trigger variants) and had the hammer dropped on it several hundred times. The hammer face is angled to distribute force across a wider area. The design has a very small amount of looseness when in the AR to allow for imperfections in printing. Video of use at https://youtu.be/KBQWYNl6mGg.

Was inspired by the AR-15 TRIGGER PULL TEST BLOCK by PrintedFirearm (https://www.thingiverse.com/thing:991599)