They where made by this
guy (made the whole rack). I don't care if you copy them, but if you do I would make the piece that holds the clamp on longer so the clamps can't slide out away from the rail. I havn't had them come off once I got them on there, but it was a PIA to get them tightned down. The rack is strong as hell. I have had my fat 230lb ass up there before, and it doesn't budge at all.