M4 Belt attachment, shoulder bolt

I see on the site that the belt has a 10mm or 3/8 diameter opening to anchor. And a suggested anchor mechanism is a shoulder bolt. How tall does the shoulder of the bolt need to be? I assume shorter is better so there’s less vertical play?

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Ideally there would be no vertical play and the belt would attach at roughly the
leve that it is on the sled. Bar has shown all his work with the belts attaching
down at the level of the workpiece (or the back of the spoilboard in some cases)

but you are correct, you want the belt to pivot, not move in other directions.
But once there is tension on the belt, I doubt that it will slip down.

David Lang

The part of the belt end which the bolt passes through is 16mm thick so you probably want at least 16.5 or 17mm of exposed bolt. Other than that the length will depend on what the anchor point looks like ie if you want to support the bolt just from the bottom or from the top too…etc

Technical drawings and STLs for the belt end anchor can be found here: 3D printed anchor point - #8 by bar