The fastest adjusting frame clamp on the market. The four clamping nuts are designed to let you make fast adjustments. They are cross-drilled to slide easily until they come up against a corner clamp, then their threads engage.
To release, just back them off by a turn and they slide again.

The corners are accurate extrusions with a machinists inside corner and provide a glue gullet. Kit includes extensions as shown giving a maximum capacity of 44" square or 65" x 23" rectangle.