Print 2 of them:

File:

QuickTolerance Test (2).stl

You should be able to measure on both X and Y:

• 5mm wall
• 5mm gap
• 10mm wall
• 10mm gap
• 20mm outer dimensions

Fit test:

• Tight fit

  ✅ Good

• Fits one side but not the other

  ❌ Check if X and Y are consistent

• Big gap fits but small doesn’t

  ❌ Check for overshooting corners (Belts, or too high acceleration), check pressure advance settings.

• Loose fit

  ❌ They have no clearance they shouldn’t be loose

• Fits but its visibly warping opening

  ❌ Tolerances are not right

• Only fits when one is upside down

  ❌ Fix elephants foot