Identifying threads can sometimes be the most difficult and frustrating part of coupling selection. However, without the right combination of threads, you may not provide a functional or safe connection.
The diameters, threads per inch (TPI) and thread pitch, etc are necessary to complete identify a thread. Ring, plug and GO/NOGO gauges are essential to accurately gauge or identify threads. In the field, in the absence of these gauges, thread leaf gauges can be used to identify the “Threads Per Inch” (TPI) and the thread pitch. On threads that you have identified to be straight threads, a caliper can be used to measure the “Outside Diameter of the Male” (ODM) or the “Inside Diameter of the Female” (IDF). A caliper can also be used to take measurements of tapered thread diameters. However, these are more difficult to define because of taper. Fortunately, there are only a handful of tapered threads to deal with and these can usually be identified from the nominal ODM and TPI.
However, identifying the thread may not fully identify a fitting series or the mating part required. The application is the primary limiting factor on the thread type used. Mid-America offers products with a variety of threads used with tubing, hose, pipe and hydraulics.
When attempting to choose a fitting, it is always advisable to first identify the thread to which it must be connected. This may entail checking with a fitting or equipment manufacturer.
When it is not possible to identify the thread:
1) Determine the number of thread per inch by measuring the distance from peak of thread across the largest number of whole threads. Then divide the number of threads by the measurement (This will provide the TPI).
2) Check to see if the thread is straight or tapered.
a) Straight Threads: Measure the “Outside Diameter of the Male” (ODM) or the “Inside Diameter of the Female” (IDF), from peak of thread to peak of thread.
b) Tapered Threads: Measure the “Outside Diameter of the Male” (ODM) at the large end and the small end, or the “Inside Diameter of the Female” (IDF), at the large and the small end, from peak of thread to peak of thread. Then measure the “Outside Diameter” (OD) of the unthreaded pipe.
Once the application and these two pieces of information have been determined, the thread can generally be determined. When in doubt, contact our technical sales support staff.