| br>i would really recommend that you:
1. buy a cheap pocket slide caliper. i got mine for less than $10.
a caliper allows you to measure diameters inside and out relatively precisely.
it looks kinda like this one:
2. buy your hardware and hold it in your hand before you design the panel!
3. measure your hardware with the caliper to get *exact* sizing so there is no confusion. front panels are too expensive to make mistakes.
4. design your panel. make a wireframe print. do a sanity check--lay your hardware out on the printout. do the jacks, pots, leds and switches all fit together? account for the mounting rail lip distance.
4. if you make a hole too small, you can always bore it out with a hand drill, a unibit, and a piece of wood to screw your panel into.