Nine times out of ten when a printed upgrade part does not fit, people blame the STL and start scaling it in the slicer. That is how you end up with a part that is wrong in a new way.

Here is the actual order to check.

First, horizontal expansion. Most desktop printers squish the first few layers and push plastic outward, so a 5mm hole comes out at 4.7mm. Print a small test clip with known dimensions, measure it with calipers, and if it reads consistently over, set horizontal expansion to about negative 0.05 and try again. This single setting fixes more fitment problems than anything else.

Second, elephant foot. If only the bottom two millimetres are tight, it is bed squish, not the model. Raise the nozzle a hair or enable elephant foot compensation.

Third, material. PLA parts near the hotend will creep and deform over a few hours of printing, so a bracket that fit perfectly on the bench will be loose by week two. Print anything within a few centimetres of the heat block in PETG or ABS.

Fourth, and only now, the file. If you have ruled out the three above and it still does not fit, the model is genuinely wrong for your machine revision. Printer manufacturers change mounting patterns between hardware versions without changing the product name, which is why a part labelled for your printer can still be wrong.

Scaling should be the last resort, because scaling a part to fix one hole changes every other dimension with it, including the screw pattern you were not having trouble with.

I build mod and upgrade STLs for Ender 3, Prusa MK4 and Bambu P1S machines, and half the messages I get are fitment problems that turn out to be horizontal expansion. Run the test clip before you blame the model.