Long bar double clamp. By LIANIUM. 11:14 video:
https://www.youtube.com/watch?v=sMxZPmWKsro
Related:
Claw Clamps by thehomeengineer
21 plans for homemade clamps
Harbor Freight Drill Press Clamp Improvements by rgsparber
Cotter Clamps by Occasional machinist
