Yes, we are here!

In times like these our hobbies become lifesavers. At GAS ENGINE MAGAZINE and FARM COLLECTOR, we have been tracking down the most interesting and rare vintage farm machines and collections for more than 80 years combined! That includes researching and sourcing the best books on collectibles available anywhere. Our online store is open and we are here to answer any questions you might have. Our customer service staff is available Monday through Friday from 8a.m.-5p.m. CDT. We can be reached at 1-800-888-9098 or by email. Stay safe!

Thread Standards Concerns

| 3/13/2018 12:00:00 AM


Restorers of old engines and machinery inevitably run into problems involving thread or fastener standards, the most common being the 1/2-12 UNC standard that appears to have been used before World War I. I have not seen this standard on anything built after about 1918, when it changed to 1/2-13 UNC. In the British Whitworth threads, the 1/2-12 BSW continued until Whitworth was effectively abandoned in favor of metric in the early 1970s. Yet even standard sizes can vary slightly, which leads me to assume that many early manufacturers made their own taps and dies and didn’t always adhere to national standards. In addition to thread standards being “loose,” I have come across nuts or bolt heads with unusual hex sizes, sometimes made to the nearest 1/32 inch.

A frustrating thread-related problem recently occurred restoring a 4 hp Excelsior engine, where I found that all the tapered pipe threads used on the fuel tank, fuel pump, mixer and return circuit were oversized. The threads on a modern fitting bottomed out before they mated up. Clearly, Excelsior made their own taps and chose to make them about 1/32 inch oversized!

To overcome this, I purchased a taper turning attachment for my Hardinge lathe in order to custom make the oversized tapered pipe fittings. This attachment has since come in very handy for producing British Standard Pipe threads. Anyone owning or contemplating owning an English engine will find the common use of BSP threads. In every case the Whitworth thread angle is 55 degrees and in almost every case there is a different number of threads per inch. The basic pipe size and taper are the same, which means you cannot visually tell the difference between NPT and BSP. Don’t make the mistake of thinking a few extra turns of Teflon tape will fix the problem!

NPT and BSP are the only two tapered pipe thread standards in the world. Modern machinery uses one of the two, and you might be surprised to know that machinery (CNC lathes, milling machines, etc.) made in Taiwan or Japan is quite likely to have BSP threads used on the various hydraulic components.

I have experienced some real disasters that occurred at the port of entry where accessories are added before shipment to the end customer. Unfortunately, there is no color coding or distinguishable marks to alert technicians to the lack of interchangeability, and the inevitable happens. I never cease to be surprised at the number of “experienced” engineers and technicians who believe there is a metric pipe thread system or that BSP is metric: neither is true.


Gas Engine Magazine A_M 16Gas Engine Magazine is your best source for tractor and stationary gas engine information.  Subscribe and connect with more than 23,000 other gas engine collectors and build your knowledge, share your passion and search for parts, in the publication written by and for gas engine enthusiasts! Gas Engine Magazine brings you: restoration stories, company histories, and technical advice. Plus our Flywheel Forum column helps answer your engine inquiries!

Facebook YouTube


click me