How can I decrease the thickness of a wall in an STL file? There seem to be a lot of search results answering the question of how to increase wall thickness, but how can I decrease wall thickness? I have an STL model of a mechanical keyboard key where the outside dimensions are correct, but the walls are slightly too thick so the key gets stuck in the down position. I'd like to shave some of the thickness off of the inside of the walls to better match the original key I'm replacing, while leaving the rest of the model dimensions as-is. How can I go about doing this? I consider myself technical in general, though I'm a novice at 3d modeling software.
The process is rather simple:


import your model into either a modeling software (e.g. Blender et al.) or a CAD-program (e.g. fusion360, Design Spark Mechanical et al.) that can import and export STL.


if needed, convert the STL into a useable model with your chosen program's functions or switch to edit mode.

select inner walls and extrude them the desired amount.
export as STL again.