Dowel Pin Tolerance and Fit Standards

May 5, 2024

Here is an article written by our engineering team that will guide you on tolerance/fit guidelines for dowel pins. We hope to give you a succinct yet complete depiction of guidelines for different use cases. Please note that these are only recommendations and sound engineering judgement must be applied while taking a decision regarding form and fit for your assemblies.

1. What are dowel pins?

Dowel pins are cylindrical pins usually made of steel, aluminum, or a variety of plastics. They are commonly used in precision engineering to locate parts in large assemblies. Dowel pins usually have diameters or lengths controlled very tightly (e.g., to the range of +- 0.010 mm or above). Combined with deep engineering know-how and knowledge of GD&T, dowel pins are small, but very powerful elements of a precision assembly.

Example of dowel pins. (Credits: PIC Design)
Example of dowel pins. (Credits: PIC Design)

2. Different kinds of fit’s

Fits refer to the coupled mating tolerance of 2 components, in this case a dowel pin and a dowel hole. There are a few different kinds of fits, and they vary depending on the overlap between two features. Generally, the fits are also dictated by the material that the dowel pins are inserted into. We’ve broken down the tolerances into 3 basic families here:

2.1 Clearance fit

A clearance fit means that the shaft (dowel pin) is smaller than the hole and there is always a “clearance” between the two. Clearance fits are preferred in situations when 2 components of a mating assembly have to be put-together and taken apart multiple times.

2.2 Interference (press) fit

Interference fits are known as press or friction fits as well. Commonly used on parts that have to hold a dowel in tightly. You may need to use a press/mallet to knock in pins if you choose an interference fit.

2.3 Transition fit

Transition fits lie in the middle of interference and clearance fits and are amongst the most commonly used fits. Tolerances of the dowel pin and corresponding holes are set in a way that it may be possible to obtain a clearance or interference fit within the specified tolerance.

3. Fit Guidelines

Here’s the fit guidelines that we suggest. Please take note that this information has been consolidated from multiple sources and prior experiences of our engineering team. Do exercise your engineering judgement before setting the tolerances for your parts. These tolerances conform to ISO 286–1-hole fit standards at mid-tolerance.

3.1 Dowel Depth

It is advised that the depth of an interference/transition hole is at least 2 X Dowel Diameter. Do add an additional tolerance for the chamfer (0.20 mm-0.40 mm) while specifying the depth of the blind hole.

3.2 Dowel Hole Sizes

These dowel hole sizes are to be used with an m6 dowel (which are the most common). If you are using a dowel pin with a different tolerance value then you may refer to the ISO fit standards to make a decision on the tolerance to call out.

Dowel Pin Fit Standards (Credits: O’Reilly)
Dowel Pin Fit Standards (Credits: O’Reilly)

4**. Dowel Pin Callout**

Here’s how you should call out dowel pin holes on your drawings. This is what we recommend. You’re free to decide on your own methods.

Dowel Pin Callout Example
Dowel Pin Callout Example

Thanks for reading!