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I'm somewhat curious as to how to use a nylon shoulder washer with a bolt. There is an example of this here (https://electronics.stackexchange.com/a/45579/95654), but I can't figure out how it would stay attached to the board. The diagram does not imply that the washer is threaded, so the hole is large enough to fit the washer (without any teeth to hold it) and ensure that the bolt does not close any circuits, but then how does it not fall out if it was inverted/sideways? Even if there was a nut at the bottom of the bolt, I still can't see how it would be stable.

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enter image description here (source: Heatsink mounting kit)

The shoulder washer is intended for bolting a TO-220 to a heatsink (or some other metal part) while maintaining electrical isolation with the heatsink. There is usually a nut on the other side of the heatsink, or the screw hole is threaded.

If you are attaching the TO-220 to a part of your PCB that has no traces, then you don't necessarily need the shoulder washer. The PCB material under the TO-220 would act as an isolator.

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Using the schematic option produces ugly results, but I hope the following diagram will help.

schematic

simulate this circuit – Schematic created using CircuitLab

It shows a bolt passing through a single layer of material, with a sholder washer on each side, and a nut, all in cross-section. When the nut is threaded onto the bolt, the washers are held in place.

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I'm on my phone, so I can't link to a website that might show a picture.

A Shoulder Washer is normally used in conjunction with either a flat washer (thin material) or another shoulder washer (thick material).

The hole through the material is very slightly larger than the diameter of the raised part of the shoulder washer. This shoulder keeps the washer centered in the hole.

The most common use that I have had for shoulder washers is when mounting power transistors to a heatsink or metal chassis.

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  • \$\begingroup\$ Yes, I understand that the ring around the neck of the washer is resting around the hole. In other words, it can't fall through. However, if the board is inverted, how is it going to stay if it does not have threading? \$\endgroup\$ – Sarah Szabo Apr 12 '16 at 0:36
  • \$\begingroup\$ you usually have a nut on the other side, probably with its own washer \$\endgroup\$ – Wesley Lee Apr 12 '16 at 0:38

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