I would like to make some of these parallel clamps that use a pipe for the bar.
The one advantage that commercial parallel clamps have over these is that the clamp faces will always line up; with the Bellevue Woodshop design it is possible to rotate the moving piece so the faces don't line up.
My thought is to glue a small rectangular strip of wood under the pipe along its entire length, and cut a corresponding space (keyhole?) out of the moving part of the clamp. Is this a reasonable solution? Is there another way to prevent the clamp from twisting? Or should I reconsider trying to prevent this twisting?