Summary

A major issue when designing and printing holes for fasteners like screws and bolts is dimensional accuracy. With filament printers, the hole you specified in a design is not quite the hole you get in a physical print. Tolerance and accuracy can vary, depending on your particular printer and material you're using. To get good results, you probably need to experiment a little and compensate for variables. Add to this, the additional tolerances that are out of your control like a fastener vendor's quality control. I have seen sets of small stainless steel bolts made in China that are consistently undersized when measuring the major thread diameter with calipers.

The Hole Gauge here is a handy tool for checking your printers results with the fasteners you have available. Gauge holes start at 5.4mm and decrease in 0.2mm increments, ending at 1.4mm. Print this gauge for a baseline to see where you are. BTW, if you can consistently print good holes under 1.5mm, you are doing well.

Easily determine the correct snug pass-thru hole size for your fasteners. Knowing the correct tap hole size and comparing it using calipers to the results in this gauge eliminates guesswork. If you intend to self-tap your screws into a softer plastic part, look for a hole with approximately 95% of your thread's major diameter. If you're working with Heat-set inserts, look for a hole with approximately 98% of the outer diameter of the insert. If you find this useful, please let me know.