Measure your wrenches with a caliper, then enter those measurements into openSCAD. The spacers are sized for M4 bolts/screws, but I just used some random screws that I had on-hand. Original instructions mention using a M4 tap, but I didn't have any problem just letting the screws cut their own threads.

For smaller holders, the number of spacers can be reduced to 2.

Printed with 0.3 layer height, 0.4 nozzle, no supports, PETG.