For protecting a valuable select-fire receiver, or even a semi-auto receiver that has seen a high volume of fire, these non-rotating trigger and hammer pins are a must. Anti-creep retainers keep the pins from constantly rotating during extended firing sessions and weakening the receiver walls. The 0.1555" diameter option is for use with Standard Small Pin receivers with enlarged hammer and trigger pin holes. Modification II pins retain the popular original "dogbone" look of Generation I pins, with added strength for longevity. Not compatible with Jewell match triggers.