You can use this test to check whether the studs for Brick-compatible parts are the right size for 3D printing. 

According to many sources, the diameter of the studs is 4.8 mm, I measured 4.9 with a caliper, but only studs with 5.0 had the necessary grip on my 3D printer. I had wasted a lot of filament to find this out. 

With this test, you can check this beforehand and don't have to worry so much about too loose or too large studs.

Alternatively, I have also uploaded the same test as a minifigure display base so that you can use the 3D printed parts afterwards. The diameter of the studs is shown on the underside of these parts.

Please note that the bottom of the parts is filled and not hollow for faster printing so they cannot be placed on top of bricks.