Installing an endpin jack | stewmac Most endpins are installed in a tapered hole to match the taper of the endpin. The reamer follows the existing hole, enlarging it by degree until the large, non-tapered, cutting flutes complete the bore to 1/2" (the outer diameter of endpin jacks). Guitar Shop 101: The ABCs of Output Jacks | Premier Guitar Mar 25, 2016Secured externally with a nut and threaded strap button, this jack replaces the guitar’s endpin. Barrel jacks can have mono, stereo, or TRS configurations. Takamine acoustic-electrics, as well as some other acoustic-electrics, use flange jacks.