Unfortunately it seems impossible to use sketches on this forum otherwise I would send sketch of clamp type I interested in. I will have to give an example.
For example, we have an existing tubular member of some structure and we need hang something up on this member without using weld. For this purposes we could use a clamp, which will consist of 2 halves of tubular flanges with inside diameter equal to existing tubular. Each half of clamp has 2 flanges with bolt holes. Toque of bolts designated to obtain necessary clamping pressure to prevent clamp from slipping.
Is the tubing round or rectangular? Either way it may be easer to form the clamp members from cold formed bent shapes - this gives you the freedom to specify an exact diameter or rectangular cross section, since matching O.D. to I.D. is not easily obtained in stock tubing sizes. The bolting flanges can be formed in the same process - eliminating some nasty welding problems. As a rule of thumb, when you draw the cross section of the material, outside bend radius equals 1.5 times the thickness of the material. Half round shells can be bumped to radius on a press brake. There are limitations - the smallest flange may be 4 times material thickness. Riser clamps are a narrrow cruder version of this idea.