A clamp 2 for flanged tubes comprises first and second arcuate portions 4a, 4b hingedly connected together, and a ratchet mechanism for locking the two arcuate portions 4a, 4b in a closed position. The ratchet mechanism comprises a linear rack 18 provided with the second arcuate portion 4b and a pawl 28 provided with the first arcuate portion 4a for receiving the linear rack 18. The linear rack 18 comprises asymmetrical teeth and the pawl 28 comprises a plurality of fingers 36a, 36b which are biased into engagement with the teeth of the linear rack 18. A second aspect features the pawl 28 being formed from a module that is detachably connected to the first arcuate portion 4a. A third aspect features the arcuate portions 4a, 4b having a hinge arm defining a recess, a shaft received in the recess in a snap-fit manner, and a cam surface on one of the arcuate portions which contacts an opposing surface of the other arcuate portion during a transition between an assembly position and an open position to force the shaft towards the hinge arm. The linear rack 18 can comprise plural toothed paths, which can each be different.
