The Ford Barn

Terry, NJ · 07-27-2017, 02:30 PM

12 X 24 T.P.I. TPI is shorthand for Treads Per Inch, That's what's known as the Pitch. The 12 is the Diameter. This is an old British system, like the gauge of a shotgun. It's based on a Gauge system , and it has no relation to sheet metal gauges. Sheet metal and shotguns actually get smaller as the numbers go up. Screw sizes get larger. Ford Model A s have a lot of seemingly weird thread sizes in/on them. These threads are almost obsolete and discontinued, but not quite. For instance, where do you find 9/16 X 16 in daily life? Or 11/16 X 16. Engineers today would be happy with a 5/8 X 11 in both cases, or maybe a 5/8 x 18 sae NF. But not Henry! And then the are the French built, Zenith Carburetors, All metric !. And the strangest of all, The cam locking screw in the distributer. Don't lose your's, You ain't gonna buy another at Lowe's or even NAPA. Why this isn't a 3/8 or 5/16 X 24, I will never understand! 12 X 24s may have been more common in the 1920s. But this screw has, like 1/4 X 20, too small a "Root" Dia. Root dia. is the dia. at the bottom of the Vee that is the thread. I'd like to revive the almost gone, 1/4 X 24 thread. If nothing else, there'd be fewer broken taps.
Terry

07-27-2017, 02:30 PM	#1
Terry, NJ Senior Member Join Date: May 2010 Location: Bucks Co, Pa Posts: 3,749	Henry's Bizarro threads! 12 X 24 T.P.I. TPI is shorthand for Treads Per Inch, That's what's known as the Pitch. The 12 is the Diameter. This is an old British system, like the gauge of a shotgun. It's based on a Gauge system , and it has no relation to sheet metal gauges. Sheet metal and shotguns actually get smaller as the numbers go up. Screw sizes get larger. Ford Model A s have a lot of seemingly weird thread sizes in/on them. These threads are almost obsolete and discontinued, but not quite. For instance, where do you find 9/16 X 16 in daily life? Or 11/16 X 16. Engineers today would be happy with a 5/8 X 11 in both cases, or maybe a 5/8 x 18 sae NF. But not Henry! And then the are the French built, Zenith Carburetors, All metric !. And the strangest of all, The cam locking screw in the distributer. Don't lose your's, You ain't gonna buy another at Lowe's or even NAPA. Why this isn't a 3/8 or 5/16 X 24, I will never understand! 12 X 24s may have been more common in the 1920s. But this screw has, like 1/4 X 20, too small a "Root" Dia. Root dia. is the dia. at the bottom of the Vee that is the thread. I'd like to revive the almost gone, 1/4 X 24 thread. If nothing else, there'd be fewer broken taps. Terry