Threaded Hole Location Gages

Our Precision JO-PLUGS® are made from wear-resistant Graph-Mo # 06 oil-hardening tool steel and hardened to 60/62 Rockwell. Calibration can be performed at customer determined intervals to verify dimensions over time. Solid threads do not bend or break.

As opposed to the tedious task of measuring the minor diameter of an internal thread with a CMM, JO-PLUGS® offer a practical, accurate and time-saving solution. With a .625 long gaging diameter, the CMM probe can take a high and low reading to determine perpendicularity in addition to true position. Independent studies have verified repeatable and reproducible results. The accuracy of our gages has made us the “go-to” company for America’s most discerning Quality labs.

An essential feature of the JO-PLUG® is a solid thread form with a pitch diameter that is measurable using the universally accepted three wire method. Precision thread grinding and inspection is performed in a third-party ISO 17025 Accredited facility. Pitch cylinders are a constant number and are ground to the minimum p.d., or “Go Basic,” of Class 2B and 3B internal threads. Flank angles are a constant 30ׄ° and symmetrical to form 60° threads to match internal threads. Pitch cylinders are critical in mating internal and external threads as stated below.

ASME Y14.5-2018, “Dimensioning and Tolerancing,” Section 2.9 states that “each tolerance of orientation and datum reference for a screw thread applies to the axis of the thread derived from the pitch cylinder.” The positional tolerance method (Section 2.1.1.1) states that the pitch cylinder is the default condition. Rarely will a minor diameter of the internal thread be used.

Most applications for threaded hole location gages consist of a surface perpendicular and accurately finished to the threaded hole datum feature. When the JO-PLUG® is seated, upward pressure on the thread flanks, which are held to a tight tolerance, make JO-PLUGS® self-center.  Finger-tight insertion provides sufficient force to hold the gage in place. JO-PLUG® threads are solid and do not flex to cling on the internal thread flanks at varying angles and degrees of pressure. JO-PLUGS® are manufactured from wear resistant tool steel, are not subject to material fatigue or breakage. Precision gages must be calibrated between centers and are inspected at intervals to meet customer requirements.

Another important element in the design of the JO-PLUG® is that the gaging cylinder, or shank, of the JO-PLUG®. The cylinder is parallel to the axis of the pitch diameter and is an industry leading .625” long. The length aids in determining perpendicularity and offers an extended projected tolerance zone, which allows numerous circle paths or straight-line data points to be collected while determining positional tolerance of Unified, Metric and HeliCoil® threads.

Pitch diameters of precision gages are commonly measured between centers and are a constant number. The JO-PLUG® utilizes a solid thread form with specified pitch diameters meeting Unified, Metric, and HeliCoil® specifications. JO-PLUG® thread flanks are solid, do not flex and locate on the internal thread flanks with varying degrees of pressure, not considering the pitch diameter. The gaging cylinder of the JO-PLUG® is an industry leading .625” long. This aids in determining perpendicularity and projected tolerance zone, as numerous circle paths and data points are collected. Most applications for centerline location gages involve a surface perpendicular and accurately finished to the threaded hole datum feature. When the JO-PLUG® is seated, upward pressure on the thread flanks, which are also held to a tight tolerance, make JO-PLUGS® self-center.  Finger-tight insertion provides sufficient force to hold the gage in place. Repeatability and reproducibility are accomplished yielding positive quality results.