Applications for Thread Gages

Thread Gages

Thread gages are instrumental in quickly and accurately ensuring tapped holes, nuts, bolts, and screws adhere to the strict tolerances required in most manufacturing operations. Their use often can provide the first indication of tooling or setup problems, tool selection mistakes, bell-mouth openings, or burrs.


Gages are used to determine whether the threads on externally threaded parts (screws and bolts) conform to the threads on their complementary internally threaded parts (nuts and tapped holes). GO/NOGO threaded gages accomplish this by determining the correctness of the thread’s pitch, lead and angle. The gage for a particular part is calibrated so the GO portion “fits” correctly manufactured parts and holes and the NOGO portion does not.

Thread Plug Gages

Used to test internally threaded products, thread plug gages often have both the GO and NOGO sections attached. To differentiate between the two, the GO portion is longer and in larger sizes contains a chip groove for easy cleaning. Without applying significant force the GO portion will completely thread onto nuts that are within tolerance. The NOGO portion will fail to engage a “good” part for more than three full revolutions before binding up. When a part passes the GO test, the hole is large enough to accept its matching shaft without undue stress. When it fails the NOGO trial, the hole is small enough to allow a strong, tight fit. Both these conditions must be met for hole or nut to fall within the specified tolerance.

Thread Ring Gages

Conversely, ring gages test the precision of externally threaded pieces. Again, the bolt is considered within tolerance when it threads completely through the GO ring but engages the NOGO ring by fewer than three revolutions. Solid ring gages determine the thread pitch and diameter acceptability calibrated to a specific thread set plug or master, which should be purchased along with the ring. Adjustable ring gages can be calibrated and re-calibrated after extended use, shipment, exposure, or other condition that could cause its settings to change slightly.

Setting (Master) Gages

Distinct from “working” plug and ring gages, master gages are not meant to be used in directly testing parts because of their exacting tolerances. Instead, they calibrate new ring and plug gages and check their continued accuracy periodically over their functional lives. A setting plug is required in order to manufacture and certify a thread ring gage, and the GO/NOGO set plug is normally ordered along with its corresponding ring.

Plug Gage Styles

Plug gages can be differentiated by the method used to hold their threaded members in the handle. Taperlock thread plug gages attach by wedging the shaft into the handle. Somewhat more expensive, reversible gages can be turned around by loosening the handle clamp and inserting the worn gage threads and bushing into the handle. The unused section – previously housed inside the handle – then becomes the working end, giving reversible gages extended life.
Large gages often are sold in reversible trilock configurations, where the gage is bolted to the handle. Because of their size and weight, trilock GO and NOGO gages are generally sold as separate units.
Contact us today for more information about the Thread Gages we offer at Regal Cutting Tools.