Bolts for Linear Rail?

[Tenson]

That's interesting, thanks!

Here is a photo of one rail (click to biggy). I don't know if you can tell that the bottom of the hole is not 100% flat, it has a very gentle chamfer, like it was drilled rather than milled out with a flat bottom end-mill. I think it is less steep than a standard screw countersink, but also not 100% flat.

I think what I'll do is just use a soft washer under the screw head to allow it to seat nicely.