Fits, Clearances & Tolerances

A fit describes how a shaft sits in a hole. If the hole is larger than the shaft the difference is a clearance — the parts slide together (a running or sliding fit). If the shaft is larger, the difference is negative: an interference (press) fit that must be forced or shrunk together and grips tightly. When the limits overlap so it could go either way, it's a transition fit. Tolerances on each part set the range of possible fits.

• Try this: Make the hole bigger than the shaft. What fit type appears, and what is it used for?
• Try this: Make the shaft bigger than the hole. How would you actually assemble an interference fit?
• Try this: Set them almost equal. Why is a transition fit harder to guarantee on the shop floor?