Was helping cousin hang a pendant type light fixture over the weekend. Fixture came with solid downrod that screwed together with those nipples that are used all over the place in lighting. I thought to myself, "self, if I had a tap for that thread I could make the rod any length she wanted, and not be limited to the foot-long increments that come with the fixture." Well, she was happy with no downrod at all in the location it was going (hung from bulkhead over kitchen sink) but it got me thinking, what the heck *is* that thread? Google suggests it is a "straight pipe thread" but what size? Does anyone make sets of those taps for a reasonable price? Even McMaster-Carr only sells them individually (for over $20 apiece!)
Nate... I do a lot of desk lamp building and repair. The size is 1/8 X 27 thread per inch. Ace hardware will have both taps and dies. 1/8 x 27 NPT. (national pipe thread. WW
If they were truly ancient they may have had NPT threads because they were converted gas lamps. That is where the pipe thread standard got established in the first place but they switched to straight threads for flexibility and convenience. The fact that so many lamp parts are available in so many shapes and colors did create the whole hash pipe market.
Being able to thread the outside surface of a rod or hollow tube using only a tap would be a neat trick man...
What you are looking for is called a die... ============================================== This is a job for Einstein's curved spatial taps and dies. Only $24 (does not include black hole required for powering device).
I wonder who the first guy was that held a nail up and decided - this would would better with a spiral groove wrapped all around it.
That made me curious enough to search and guess whose name popped up. It's once familiar to any of the seniors here who ever had an English car:
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" . . .moved to London where he found employment working for Henry Maudslay, the inventor of the screw-cutting lathe . . .In 1841 Whitworth devised a standard for screw threads with a fixed thread angle of 55° and having a standard pitch for a given diameter. This soon became the first nationally standardized system; its adoption by the railway companies, who until then had all used different screw threads, leading to its widespread acceptance. It later became a British Standard, "British Standard Whitworth", abbreviated to BSW and governed by BS 84:1956."
Well, s "While a recent hypothesis attributes the Archimedes' screw to Sennacherib, King of Assyria, archaeological finds and pictorial evidence only appear in the Hellenistic period and the standard view holds the device to be a Greek invention, most probably by the 3rd century BC polymath Archimedes himself.[49][dubious - discuss]"
No, I'm looking for a tap, the downrod was made of tubing with a little standard lighting nipple at each end. So if I wanted a custom length, I would have cut the tubing, squared off/dressed the end, then tapped it so the nipple could be threaded back in.
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