diamond locating pin

What are diamond locating pins and should I be using them?

No, they don’t help you locate diamonds, but diamond locating pins can be used to make assembling parts easier!

What are Locating Pins?

Locating pins are a great way to make sure the parts you are putting together fit the way you want them to fit. Drill two holes opposite each other in each part, install a cylindrical locating pin, and presto! Your parts are aligned exactly the way you want. If you are having alignment issues with using just bolts or other fasteners, a locating pin can be a great way to firm up your assembly.

Before you rush out to start drilling holes, one downside to cylindrical pins is that they only constrain parts in two dimensions. For example, one pin would prevent the parts from sliding up and down or left and right, but they could still rotate around the pin. You might say, “Just add another pin and your rotation problem is solved!” True, but if the locating pins are even slightly misaligned, they can bind and prevent the parts from coming together properly.

Diamond Head Pin

Diamond Head Pin


Diamond Locating Pins

Enter the diamond locating pin to the rescue. The diamond in the name refers to its shape – the pin is cut a small amount on four sides, forming a diamond with the original curved section on two opposite sides. This unique shape allows the pin to contact the locating hole with a smaller surface area that prevents movement in one direction (left/ right) while allowing a small change in the other direction (up/ down). Now your parts can’t rotate, and you still have a little wiggle room when assembling.

One thing to consider when installing a diamond locating pin is the orientation of the contact surfaces. If your assembly has a critical measurement that must be kept, you should align the diamond locating pin in this direction. The contact surfaces on the pin will prevent movement and keep your alignment, while allowing a small shift in the non-critical direction. Engineers and draftsmen should take care to make good notes on your drawings so your assembly crew can install the pin with the proper orientation.

Diamond locating pins can also be used for concentric parts when the rotation of the parts is not critical, but the central axises must be aligned. In this case, simply install three diamond pins on a circle centered on the part with the contact surfaces aligned radially. The two centers of the parts will then be coaxial, but the parts can be rotated slightly to aid with assembly.

In summary, diamond locating pins are almost always used along with a regular cylindrical pin (the exception being the last radial example). Together, they give you a highly accurate finished product without the binding issues common to assemblies with only cylindrical pins. While it’s true that grabbing a bigger hammer can usually solve any misalignment issue, substituting a diamond locating pin can keep those tempers low and your successful assembly quota higher.

Still confused about when you should use a diamond locating pin? Check out our website for more details on locating pins and how they’re used, comment below, or call one of our experts at 800-681-7475!

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  • Ben Bilbrough

    I’ve had success with using diamond pins, the part fits on much better.

    Does someone know how much the tolerance between the holes can open up due to using the diamond pin?

    I’m working out GD&T standards for our company and when using two dowel pins for locating, the distance between the dowels has a tolerance and the clearance between the dowels and the mating holes needs to be enough to ensure they fit together. Currently, I am using .001 true position between the dowel pins which means I need to have .0005 clearance on the mating thru holes. Wondering how much I can open up the tolerance and how to do the GD&T

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