Stand Alone Rainwater Harvesting System
What is the difference between NPS and Buttress drum threads?
by RainSaucers Inc. on May 12th, 2014

When we  started designing our first product (the 48" RainSaucerâ„¢), we had to figure out how we were going to attach it to rain barrels.  We soon realized that most 55 gallon drums had two standardized 2" bung hole caps that we could leverage called NPS and Buttress.  

Buttress unfortunately, was not so useful,  as we could not find any adapters locally that were compatible. As we've learned since, this is because  the buttress standard is a highly specialized oil industry thread used because of the tight hydraulic seal it creates. 

NPS, on the other hand, was immediately compatible with the common 2" male PVC adapters from the local hardware store. NPS, which stands for national pipe straight thread, is standard not just to drums but to all piping in the United States. NPS is also referred to within the context of the National Pipe Thread standards which were invented by Amercian William Sellers in 1864 as part of wide range of standards for nuts, bolts, and screws.

Another way to distinguish between NPS and Buttress is by their appearance. Buttress caps have a thread where there the lines are spaced further apart making them look more coarse. So they are sometimes called "coarse threads". NPS, by contrast, has threads much closer together so they are often referred to as "fine threads"

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