lead pipe cinch
A “lead pipe cinch” is a sure thing, or something easy to accomplish.
“Cinch” comes from the Spanish word for a horse’s saddle-girth — cincha. A saddle that had been tightly cinched was secure or had a firm grip. The figurative sense of cinch was first recorded from the 1870s as meaning to get the better of somebody, but soon came to mean “a sure thing.”
From The Manitoba Daily Free Press, December 1882: “The next movement was to throw the bull, and then cinch a lasso and rope tightly around his body.” Considering how big and strong a bull is, that description sounds entirely too simple.
“Lead-pipe cinch” started to appear in print in the 1880s. The usage was often in contexts where the rich and powerful used their status to form monopolies or indulge in insider trading in order to cheat the general public. The Illinois newspaper The Morning Review, December 1889: “The briber and bribed would sit down to a game of poker and a ‘lead-pipe cinch’ was nothing to the sure thing the legislators had.”
It appears that a “lead pipe cinch” is better than just a plain “cinch,” so “lead pipe” is what grammarians call an intensifier. One explanation is that a cinch was a form of joint used in plumbing and that a lead-pipe cinch was a secure joint. Another is that if a leather cinch was effective, one made of lead would be even more so.
On the other hand, perhaps “lead pipe” was chosen simple because it sounds unbreakable.
There are examples of other intensifiers for cinch, which would hardly be likely if “lead pipe” had a special meaning. In 1891, Maitland’s Slang Dictionary refers to “leadpipe” and “grapevine” as intensifiers for cinch. A grapevine is secure? But I’ve never met a grapevine, so perhaps it is more secure than the word “vine” would imply.
In October 1891, The Daily Morning Republican listed a number of “cinch” superlatives to describe a bettor’s certainty that his horse Firenzo would win the next day: “The track will be heavy tomorrow, and I’ve got a copper riveted, lead pipe, copyrighted, air tight cinch. Firenzo in the mud — she swims in it.”
It’s a lead pipe cinch that Firenzo had Teflon hooves that slid in and out of mud as though it didn’t exist.