When supporting a pipe, what is important the OD or the ID?

OD of pipe as any support ( shoe, trunoion or any other type) are from steel top to pipe OD

For pipe to pipe coneection I.D is important.

It goes without saying that OD is important for pipe supporting.Supports connect or attach to OD of pipes.

Whenever we support a pipe using clamps or trunnions the size selected will depend on the O.D. of the pipe.In case of clamps, its the bolting arrangement that holds the pipe and in case of trunnions we will require the thickess and the OD for the trunnion size calculation.

OD remains constant while ID varies, So OD is important than ID.

pipe support is importane of outer side diameter.

in the important supporting is OD 

Outside Diameter of the Pipe