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

Re: Henry's Bizarro threads!
 

Stupid trivia that is vaguely related... I don't know about sheet metal and wire gauges, but shotgun gauges are based on the weight of lead balls, as in the number of lead balls at a given diameter that equal a pound. So, twelve lead balls the diameter of a 12 gauge shotgun bore will weigh a pound...twenty lead balls the diameter of a 20 gauge shotgun bore will also weigh a pound. The same is true for 10 gauge, and 28 gauge. 410 is the exception that proves the rule.

Ken

Re: Henry's Bizarro threads!
 

Who cares..

Re: Henry's Bizarro threads!
 

I have a bucket of old nuts and bolts where they are a new size exactly between SAE and metric! Didnt start off that way but mother nature has a way of modifying things.

Re: Henry's Bizarro threads!
 

Re: Henry's Bizarro threads!
 

Pitch is the inverse of TPI, and vice versa, in the standard system.

But, yeah, I feel your pain.

Re: Henry's Bizarro threads!
 

Buster T.:cool: HOWLS, like an Old Wolf, when he hears really high PITCHED sounds:confused: Nothing to do with threads!
Bill W.

Re: Henry's Bizarro threads!
 

I find the "gauge" system of threads a mystery. I have never seen it here so I wonder about it being British in origin. For threads smaller than 1/4", the British used the BA range (British Association). I suspect it is a uniquely American animal.
With the introduction about 60 years ago of the metric system here, all this became academic anyway except when I have to go back nearly 90 years with my Model As.:D

Re: Henry's Bizarro threads!
 

I think this supplier is a solution to the problem.

Roy Nacewicz Enterprises
www.fordbolts.com

Re: Henry's Bizarro threads!
 

I don't understand your confusion. 12-24 is a 7/32 diameter with 24 threads to the inch. Keep in mind that there are presently the most frequently used sizes being categorized as National coarse and National fine. There are however categories Xtra fine and threads classified as pipe taper and pipe straight. There are Acme threads, double pitch, and triple pitch. Get an SAE engineers book which will list the standards used by the auto industry as well as others giving the sizes. Taps and dies are also classified by thread fit GH2,3,5 for oversizes as well as adjustable dies to acquire a certain fit. Theres quite a bit tobe learned on the threading of our bolts, nuts and screws not to mention Grade 2, 5, and 8 for bolt strengths.

Re: Henry's Bizarro threads!
 

Throw some screwball size gun screws and their heads in there:p

Re: Henry's Bizarro threads!
 

WOW! I just looked in my "Machinery's Handbook" 14th edition, (1950) where all threads and threading systems (Non Metric)are listed and I ran across the BA system. Curiously, it runs like shotgun gauges. the higher the number, the smaller the diameter, beginning with 0 Ga, at 6MM coming down to 23 Ga at .0.33 MM or about .013 diameter, pretty small! I'd hate tap something like SS or Titananium in that thread. However, I could find nothing about the "Gauge" system as used in American threads (000 to 14?)
Terry

Re: Henry's Bizarro threads!
 

I am not confused! I started this thread for the sake of those who are new to the hobby and encounter some of these screws and wonder just what they're dealing with.
Terry

Re: Henry's Bizarro threads!
 

OK, So who has 12-24 Robertson Head Countersunk head bolts for the Floorboards. The trick is getting the length. I even tried Robertson Screw in Milton, Ontario and they don't have them.

John Poole

Re: Henry's Bizarro threads!
 

For some reason, the Metric Gurus adopted the British BSP pipe thread system.

Re: Henry's Bizarro threads!
 

I knew BA was identified by a number for size but didn't realise they ran like shotgun gauges. They are hardly used these days.
BTW, When Whitworth designed his thread system which is the same as NC (except for a 55 degree thread form vs 60 deg and 12 vs 13 TPI at 1/2") the smallest was 1/4" It was intended that for smaller sizes, BA would be used. These days we see smaller sizes labelled Whitworth but they are someone else's fake creations.
When the metric system of threads was devised, they didn't bother changing some threads already in use, like BSP as observed above.
Just imagine how complicated the world was before Whitworth standardised things so far as coarse threads are concerned. The British fine thread system was BSF (British Standard Fine), also a standardised system. Then along came NC and NF - nearly the same but but not quite so standardisation was put backwards by years. I predict that eventually, the whole world will adopt the metric system but for now, I'm just pleased that my lather has a 127 tooth gear for the headstock.

Re: Henry's Bizarro threads!
 

I see most scale model Steam engines use BA.

As for "Bizarro" it was not strange at all during the time the A's were built.

Re: Henry's Bizarro threads!
 

Yes, when I was building my walking beam steam engine, it had the BA screws and I had to buy taps to match.
I broke a tap in one of the pieces, and that will make you learn a few new words trying to get it out.:eek:

Re: Henry's Bizarro threads!
 

20 years ago when I worked for pietros pizza. The can openers( mounted on a table, with a crank handle) used # 12 screws slotted. Don't remember the thread count, it I still have a box of them in my truck.

Re: Henry's Bizarro threads!
 

In my 20 + years as a machinist, Toolmaker, and Model Maker, not to mention sort of a jack of all trades, (Boats, Airplanes, farm machines) I only can recall running into 12 X 24 twice! Put the screw up against a 5/16 X 24, if the threads mesh , it's a 24 T P I , Dia. Notwithstanding.
Terry