Helps with accurate and square drilling. 10mm, 8mm, 6mm, 5mm, 4mm, 3mm, 2mm.

External 1mm lines to aid accurate centering.

Heights of 20mm, 15mm and 10mm to suit the length of drill bit, also 20mm deep with a 10mm V cut for tubes.

I've found it helps to smear the base with a little hot glue to prevent it sliding when in use.

Print at 0.2mm, at least 0.8mm perimeter, floor and roof. 10%-20% grid infill.