Acertainty; inescapable fact: not early enough to move no tables, that's a lead-pipe cinch/ calls Coleco Vision a ''lead-pipe cinch'' for making a strong showing at Christmas
Something very easy; cinch, piece of cake: a lousy lead-tight cinch that any freshman in law school could have won
[1898+; fr the fact that a lead pipe can be easily bent, in case one has bet on such a feat]
The Dictionary of American Slang, Fourth Edition by Barbara Ann Kipfer, PhD. and Robert L. Chapman, Ph.D. Copyright (C) 2007 by HarperCollins Publishers. Cite This Source
Idioms and Phrases with lead-pipe cinch
A certainty, an assured success. For example, “An engagement ain't always a lead-pipe cinch” (O. Henry, The Sphinx Apple, 1907). This colloquial expression is of disputed origin. It may allude to the cinch that tightly holds a horse's saddle in place, which can make it easier for the rider to succeed in a race; or it may allude to a cinch in plumbing, in which a lead pipe is fastened with a band of steel to another pipe or a fixture, making a very secure joint.
[ Late 1800s