---
title: Interference Fit: Press and Shrink Fits Explained | Wolf Machine
url: https://wolfmachinenv.com/glossary/interference-fit/
business: Wolf Machine & Fabrication, Inc.
address: 4812 Longley Ln, Reno, NV 89502
phone: (775) 359-5570
hours: Shop Monday-Friday 7:00 am-3:30 pm; closed Saturday and Sunday
type: Metal and plastic fabrication and machining (custom and CNC machining, welding, metal and plastic fabrication, gearbox and part repair, align boring, metal spray)
---

[Photo: Stock photo: rows of round steel parts after machining]

- [Home](https://wolfmachinenv.com/)
- [Glossary](https://wolfmachinenv.com/glossary/)
- Interference fit

# Interference fit

An interference fit is a joint where the shaft is slightly larger than the hole it goes into, so the two parts have to be forced together and then hold by friction. It is also called a press fit or a shrink fit, depending on how the parts are assembled.

Stock photo: rows of round steel parts after machining

Bearings, bushings, gears and sleeves are held in place this way. There is no key, bolt or glue doing the holding, only the squeeze between the two surfaces, so the sizes on the shaft and in the bore decide whether the joint lasts.

## Press fits, shrink fits and clearance fits

In a press fit, the part is forced on with a press, and the amount of squeeze is small enough to do without heat. A shrink fit uses temperature: the outer part is heated so the bore grows, or the inner part is chilled so it shrinks, and the parts slide together and grip as they return to the same temperature.

A clearance fit is the opposite. The hole is larger than the shaft, so a bearing, pin or bushing turns or slides freely. The size difference in either case is a few thousandths of an inch or less, and the limits are written as [tolerances](https://wolfmachinenv.com/glossary/tolerance/) on the print, often with a standard fit class.

## Bearing seats and bushings

A bearing's inner ring is usually pressed onto the shaft, and its outer ring pressed into the housing, so the seats must be round, true and the right size. A bushing is pressed into a bore and is then often finished to its inside size after it is in.

Because the fit is tight, any damage to the seat shows up quickly. A scored shaft seat, an oval housing bore or a shoulder that is not square will let the bearing sit crooked or turn on its seat.

## What happens when a fit wears

When the seat wears undersize, the bearing starts to creep. It turns slowly on the shaft or in the housing, and that wears the seat even faster. This is often called a spun bearing. Signs include heat at the bearing, a discolored or polished seat, a rumble, and fretting dust.

A worn seat is usually built back up and then machined back to size, using [metal spray](https://wolfmachinenv.com/services/metal-spray/), a sleeve or weld, depending on the load and the metal. The guide to [metal spray, sleeve or weld](https://wolfmachinenv.com/guides/metal-spray-sleeve-or-weld/) compares the methods. Send the seat sizes and a photo of the worn area with your [quote request](https://wolfmachinenv.com/request-a-quote/).

### Sources

- [Interference fit (overview)](https://en.wikipedia.org/wiki/Interference_fit) (2026-10-18)

### Talk to the shop

[(775) 359-5570](tel:(775)%20359-5570)

| Monday to Friday | 7:00 am - 3:30 pm |
|---|---|
| Saturday and Sunday | Closed |

[Request a quote](#quote)

### Keep reading

- [Metal spray](https://wolfmachinenv.com/services/metal-spray/)
- [Metal spray, sleeve or weld: rebuilding a worn surface](https://wolfmachinenv.com/guides/metal-spray-sleeve-or-weld/)

## See also

[Tolerance](https://wolfmachinenv.com/glossary/tolerance/) [Keyway and keyseat](https://wolfmachinenv.com/glossary/keyway-keyseat/) [Surface finish (Ra)](https://wolfmachinenv.com/glossary/surface-finish-ra/)

## Where you will see it on this site

[Bronze](https://wolfmachinenv.com/materials/bronze/) [Metal spray, sleeve or weld: rebuilding a worn surface](https://wolfmachinenv.com/guides/metal-spray-sleeve-or-weld/) [Making a part that is no longer made](https://wolfmachinenv.com/blog/making-a-part-that-no-longer-exists/)

[Photo: Stock photo: a lathe turning a bar, hot chips flying]

## Request a quote

Tell us what you need, attach a drawing or photos of the part, and we will get back to you during shop hours. Free consultations; prompt estimates.

[Call (775) 359-5570](tel:(775)%20359-5570)

- From your specifications, drawings or samples. We can also assist you in designing your product or part.
- Free consultations and prompt estimates
- Stands behind the work: Our rates are very competitive and our quality is second-to-none. Wolf Machine stands behind the work we perform.
- Company accounts: all major credit cards, or we can open an account for your company

Shop hours Monday to Friday, 7:00 am to 3:30 pm. Send your request any time and we will get back to you during shop hours.

Stock photo: a lathe turning a bar, hot chips flying