Holey Tools is a free Blender add-on that resizes mesh holes to precise diameters — a small utility that solves a problem Blender is genuinely bad at.
Why Blender Struggles With This
Blender is a polygon modeller. It has no concept of a hole as a feature with a diameter — a hole is just a ring of vertices arranged in a circle. There is no field to type 8mm into.
So resizing one means selecting the loop, scaling it, and then measuring to check. Do that across a dozen mounting holes and you have spent an hour on something a CAD package does in seconds.
Where Exact Diameters Actually Matter
- 3D printing — a hole for an M3 bolt has to fit an M3 bolt. Print it 0.3mm undersized and the part is scrap.
- Hard-surface modelling — consistent hole sizes across a model read as manufactured; inconsistent ones read as sloppy
- CAD-style work in Blender — mechanical parts, enclosures, brackets
- Assemblies — parts that must physically mate
The 3D Printing Angle
This is where it earns its place. Printed holes almost always come out slightly undersized due to material shrinkage and nozzle behaviour, so designers deliberately oversize them. That only works if you can set an exact starting diameter.
Pair it with Blender's built-in 3D Print Toolbox — already included, just enable it — which checks for non-manifold geometry, thin walls and overhangs before you waste filament. See our guide to 3D printing model sources.
Worth Knowing
Check your scene unit scale first. If your Blender units do not correspond to real millimetres, a precise diameter is precisely wrong. Set units properly before doing any dimensional work.
Creator: amoose136 · Price: Free · Software: Blender
Useful alongside our 3D printing model sources guide and our procedural modelling add-ons roundup.