pipe wrench

from The American Heritage® Dictionary of the English Language, 5th Edition.

• noun A wrench with two serrated jaws, one adjustable, for gripping and turning pipe.

from Wiktionary, Creative Commons Attribution/Share-Alike License.

• noun An adjustable wrench (British spanner) with a toothed jaw for gripping pipe, frequently used by a plumber or pipe fitter, to loosen and tighten pipes with threaded connections.

from WordNet 3.0 Copyright 2006 by Princeton University. All rights reserved.

• noun adjustable wrench for gripping and turning a pipe; has two serrated jaws that are adjusted to grip the pipe