3/8" Drill Guide

thingiverse

Stiffening gussets are added to vertically strengthen the guide. A 9.55mm hole is drilled, which is only slightly larger than a standard 3/8 inch size. To accommodate a larger drill bit, wall thickness has been increased significantly. If your printer isn't significantly more advanced than mine, you'll still need to ream the hole down to a precise 3/8 before the drill can pass through smoothly.