Whenever gauges become the center of the conversation, most people often confuse gauges with thread gauges. Not to say it is entirely wrong, but thread gauges are actually a particular class and type in the family of gauges. The terminology is often used extensively and interchangeably due to the fact that the primary purpose of gauges is to measure what we refer to as “threads” on mechanical pieces of equipments.

    It is to measure these thread sizes, the pitch of these threads, and various other parameters such as major diameter, minor diameter, NOT GO Functional Diameter, etc. for which gauges come into play. Depending upon the type of work, there exists a bunch load of gauges and associated tools such as tri-roll comparators, thread ring gauges, metric thread gauges, ACME gauges, etc.


    Before one can explore and understand the different types of gauges, it would be more fundamental and appropriate if one first gets a better idea about the types of threads. Every thread type has its own profile and geometrics that allows them to serve different types of tasks and functionalities. The various parameters and grounds on which threads are bifurcated and distinguished are:

    • Geometrics

    The different types of geometrics (shape) include (but not limited to):
         a. Cylindrical
         b. Tapered
         c. Tapered

    • Tolerance

    The different types of tolerance classes for gauges include:
         a. Class XX
         b. Class W
         c. Class ZZ
         d. Class X
         e. Class Y
         f. Class Z

    • Measurement Unit

    The different units of measurement include:
         a. Metric
         b. English
         c. Mixed (both, for some gauges are capable of measuring threads in both units)

    • Display

    The types of display on gauges (to display and highlight information and settings of the gauge) include:
         a. No display
         b. Vernier Scale Display
         c. Direct Reading Scale
         d. Dial Display
         e. Analog Display
         f. Digital Display
         g. Column Display
         h. Bar graph Display
         i. Remote Display

    Now that we are quite familiar with the parameters through which we distinguish gauges, let us know, actually get familiar with some types of gauges. The most major of parameters used to classify gauges and select one as per the needs is the internal and external thread type through specific thread designations and ultimately the type of gauge required are understood and selected. Some of the major classes of gauges include (but not limited to):

    1. UNS
    2. UNF
    3. UNC
    4. NPT
    5. ACME
    6. Buttress
    7. BSPT
    8. BSPP
    9. NPTF
    10. NPSF
    11. ANPT
    12. BSPP
    13. UNEF
    14. UN

    So, let us discuss a little bit more in detail the following types of gauges

    1. UNEF Gauge

    Standing for Unified National Extra Fine, the UNEF thread gages is a category of thread gauges (meaning the primary motive has got to do something with threads). This Extra Fine factor in the name is the indication that the number of threads present per inch are really high for each and every size of the fastener.

    2. UNF Gauge

    Stands for Unified Fine Gauge, the UNF thread gages also have a similar work as that of the UNEF gauge. The place where they differ is in their fine-tune measurements. Where the UNF gauge can measure pitches in the range of 0.0138 inches to 0.0833 inches, the UNEF gauge is capable of measuring pitches finer than the range of UNF gauge.