zack24:
Given what appear to be four different sized holes in this clamp, my best guess is that it is used on pipes whose stems are stuck in their shanks. The clamp could be applied to the outside of the shank in order to keep it from splitting, then the stem carefully removed. If, as oft may happen, the stem's tenon were to break off in the shank, then the clamp (still in place) could be used to hold the shank vertically plumb while the tenon is drilled out.