The ideal tool to clamp frames!

Completely knurled for good grip, the speed-clamping nuts are designed to let you make fast adjustments, yet hold securely when you tighten them.
They are cross drilled to slide easily on the rods until they come up against a corner clamp; then their threads engage. To release them, you just have to back them off a turn or two and they are then free sliding again.
The speed clamp includes four corners (strong, glass-filled nylon with brass inserts), four speed clamping nuts and four 1/4" UNC threaded rods that will clamp up to 585 mm square.
To increase clamping capacity to 1,120 mm square or 1,650 mm by 585 mm rectangle, an extension set is included; it contains four 1/4" UNC threaded rods and four coupling nuts.
The rods and coupling nuts have a black-oxide finish.

https://www.axminstertools.com/veritas-4-way-speed-clamp-475309