Are tube clamps and key clamps the same thing?

Yes — “tube clamp” and “key clamp” refer to the same type of steel grub-screw fitting used to join galvanised steel tube into a structural framework without welding. “Key clamp” is a widely used trade name, while “tube clamp” is the generic descriptor. F.H.Brundle’s tube clamp fittings are fully compatible with all Key Clamp and equivalent tube component systems.