Prints turning out 'fine' and prints actually fitting with precise tolerance off-shelf components like bearings or the sliders fitting in your extrusions are 2 different things. Unless you have a Prusa printer, you should start by calibrating your printer. If you get lucky somehow and a 20mm test cube actually prints at or near 20.00mm in x/y/z than you should be fine but you first need to be able to take real measurements and feeler gauges won't do that here, you need calipers
Calipers that aren't fancy but don't suck:
https://www.amazon.com/Winkeyes-Conversion-Stainless-Homework-included/dp/B07Z1ZRTSW
It's a pain but well worth doing.. stock settings are usually juuust enough to make bearings/sliders not fit, at worst aren't even in the ballpark. You will need to be able to flash the settings on your printer, so first you need a 3rd party program that can do it. I use Pronterface.. lightweight, free and does what you need it to.
www.pronterface.com
Start by calibrating the extruder, everything downstream is affected by that so ensure it's proper first.
https://mattshub.com/blogs/blog/extruder-calibration
Next follow this guide (has links to test objects in guide..) I found 20mm cubes to be great but also used 100mm xyz thing too
https://all3dp.com/2/how-to-calibrate-a-3d-printer-simply-explained/
Once your printer is calibrated, in Cura I used 4mm walls/top/bottom, 60% grid infill and found a normal brim wasn't enough for proper bed adhesion to keep corners form lifting so modeled a 1mm thick brim around the parts since Cura only allows .4mm thickness for that.