These templates offer a consistent way to mark holes for drilling your pot calls. It is recommended you get the center drilled before you mark and drill the sound holes to make sure they are true to the center hole. These cover the most common hole spacings for 3" pot calls, 3.25" pot calls, and 3.5" pot calls/3.5" double sided pot calls. Outside edge is 3-7/8" which is a great reference point to mark for your pot calls when turning to get you close to where you need to be on the standard sizes for 3.5" surfaced calls.