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Tool Talk Discussion Forum

1/2 x 12 threads per inch tap ,ever hear of one??

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dave2pa

03-11-2006 13:41:26




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have anyone ever heard of these?? standard 1/2 inch is 13 TPI ,,but this one is 12 TPI,, I actually seen the Tap ,,seems old even has a patent date on it .og 1856 or 1866 also says USS




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Glen in TX

03-14-2006 12:15:43




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 Re: 1/2 x 12 threads per inch tap ,ever hear of on in reply to dave2pa, 03-11-2006 13:41:26  
Lots of special threads out there and that is one of them. Check out special thread taps and dies and McMaster Carr or MSC catalogs.
mscdirect.com
mcmaster.com



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[email protected]

03-13-2006 19:28:52




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 Re: 1/2 x 12 threads per inch tap ,ever hear of on in reply to dave2pa, 03-11-2006 13:41:26  
yes they were used on the rod for the pump cylinder used with a windmill back in the 1930 ds. the local blacksmith also made long bolts that thread when he needed a 1/2 13 he would come and borrow mine.



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benny2

03-12-2006 11:19:57




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 Was standard til Re: 1/2 x 12 threads per inch tap in reply to dave2pa, 03-11-2006 13:41:26  
Was used an alternate standard til 1940 or so when the 1/2 by 13 then was made the NC standard. You may find that size in production use til past those years when the old tooling was used up. You may even still find modern charts STILL listing it as NC with the 13 tpi



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JMS/MN

03-12-2006 09:53:14




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 Re: 1/2 x 12 threads per inch tap ,ever hear of on in reply to dave2pa, 03-11-2006 13:41:26  
During college I worked at a machine shop in St. Paul, made wood sanding and carving machines. Most went to furniture factories in NC, etc. Carvers used 1/2-12 thread setscrews in the pivot arms of multiple spindle machines. Why? Think the boss made a good buy on setscrews. 13 would have worked the same without confusion on locknuts.



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cdmn

03-11-2006 20:12:10




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 Re: 1/2 x 12 threads per inch tap ,ever hear of on in reply to dave2pa, 03-11-2006 13:41:26  
Threads were a mixed bag before World War One, which demanded some rational standardizaton for efficiency in military production. Screws and bolts are produced by rolling them between hard dies with parallel grooves set a certain distance apart. If you had a set for 12 threads per inch, you could roll many different diameters of blank screws through those same dies. Just change the relative angles of the top and bottom dies. For home-made threads, the lathe gearing could stay the same for different diameters. There were actually series for 4, 6, 8, 12, 16, 20, 28, and 32 threads per inch. The hole taps also could be made for different sizes using the same machine settings for all diameters. In the prewar days, you often had to buy the replacement bolts from the OEM. Some of the big companies had their own captive fastener divisions, and they made no effort to follow each other.

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Russ from MN

03-11-2006 17:41:26




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 Re: 1/2 x 12 threads per inch tap ,ever hear of on in reply to dave2pa, 03-11-2006 13:41:26  
I have an old (100+ years) tap and die set that has one. Have seen one machine in 32 years as a millwright that used them!



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Davis In SC

03-11-2006 17:41:05




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 Re: 1/2 x 12 threads per inch tap ,ever hear of on in reply to dave2pa, 03-11-2006 13:41:26  
I have run into a few of those, both on British, & Tiawanese tooling. Once, as an emergency fix, I took 1/2-13 bolts, & ran a 1/2-12 die over them. It got me by.



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J.T.L.

03-11-2006 16:04:26




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 Re: 1/2 x 12 threads per inch tap ,ever hear of on in reply to dave2pa, 03-11-2006 13:41:26  
The 1/2"-12 thread is listed as an "NS" thread which means "Special Threads of American National Form". I have run into them a number of times in the 44 years I spent as a Machinist. Even found a box of them at one of the last companies I worked for. They were brand new, and I dumped them in a bin with with the 1/2"-13 bolts by mistake. Learned of my mistake the next week when I grabbed some to use as tie-down bolts on a Bridgeport mill and the hex nuts used with the mill would not fit. There are 6 different threads for an American 1/2" bolt. The Threads Per Inch are 12, 13, 20, 24, 27, and 28.

John in Pa.

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big fred

03-11-2006 14:09:07




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 Re: 1/2 x 12 threads per inch tap ,ever hear of on in reply to dave2pa, 03-11-2006 13:41:26  
I believe what you have is a Whitworth, a now-obsolete British thread standard. If you're looking for a market for it, I'd suggest someone who collects/restores old British motorcycles or cars.



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