Big Sert Tap Guide 3/8-16 & 3/8-24 Part #75315
Big Sert Tap Guide 3/8-16 & 3/8-24 Part #75315 Works With Both Sizes TAP GUIDES INSURE THAT THREADS ARE SQUARE TO SURFACE. The lower portion of the tap guide should remain as square as possible to the engine surface. Turn the tap slowly while making sure the guide remains flush.