Taper Pipe Threads are one of the more challenging threads to produce and measure. The ASME B1.20.1-2013 Pipe Threads, General Purpose (Inch) is the current standard that covers both the part thread specifications and the gages for NPT, NPSC, NPTR, NPSM and NPSL threads.

In Geometric Dimensioning and Tolerancing (GD&T) there has been a long-standing conflict between the worlds of specification and measurement. The goal of specification is to ensure that components will function; the goal of measurement is to ensure that manufactured components meet those functional requirements. 

Thread plug gages are fascinating products when you consider the technical details that go into their manufacture and the precision they embody. To some, they look like fancy bolts and are treated accordingly. 

Screw thread inserts (STI) require the threaded hole to be inspected prior to inserting the threaded insert or coil. The dimensions and tolerances for the gages used to inspect these threads have been a bit confusing over the past 30 years. 

There’s no question about this column. I accept the blame for what appears in this monthly effort for better or worse. This column is all about the standards I often refer to in my rants. I frequently encounter folks who question the information these standards contain and sometimes the question is valid but there are ways to challenge or change technical details within them. 

Amongst the pile of tools in my garage is a nice six-inch caliper, which I use for the occasional minor project around the house. And even though I work in one of the finest dimensional calibration laboratories in the country, where we calibrate thousands of calipers every year, my own personal caliper has not been calibrated in over 20 years.

GD&T is the only tool we have with which to manage machine part geometry perfectly. In particular, it’s the only tool we have with which to impose truly functional limits of imperfection on machine part features and actually guarantee assembly and operation prior to drawing release.

Mahr Federal's Alexander N. Tabenkin was presented with the ASME 2014 Dedicated Service Award for Standardization and Testing during the ASME B46 meeting on October 24, 2014, at NIST Headquarters in Gaithersburg, MD.

Castings, Forgings and Molded Parts.