There are two styles of Heli-Coil inserts. The standard or FREE RUNNING insert which provides a smooth free-running thread; and SCREW-LOCKING which provides self-locking torque on the male member by a series of “chords” on one or more of the insert coils. They are both available in Inch and Metric series. For Standard (free running inserts), a tolerance class 5H or 2B is recommended. For Screw-Locking inserts, a tolerance class 4H5H or 3B is recommended in order to develop higher locking torques.
Our Helicoil Taperlock Thread Plug Gages, or Screw Thread Insert (STI) Gages (Made in the USA), are manufactured to an “X” tolerance and are made of oil hardened tool steel. Heli-Coil threaded work plug gages are used to inspect the hole prior to inserting a screw thread insert when repairing a threaded hole. The metric STI gauges can be class 4H5H (most commonly ordered) or 5H. We default to class 4H5H. The UN series Heli-Coil gauges can be 2B or 3B class. We default to 2B.
It is not necessary to gage the installed insert. After the insert is installed, the GO thread plug gage may not enter freely; however, the insert will always seat itself when the bolt or screw is installed and tightened. (Reference NASM33537).
When gaging tapped holes which have been thoroughly cleaned (or which have a protective finish applied) the gage should always be lubricated with a light 3-1 oil (NOT WD-40).
View description and class pitch diameters for helicoil taperlock gages. (pdf)
We can certify our gages to meet or exceed all published specifications and are traceable to the NIST (National Institute of Standards and Technology), and in compliance with (ISO) 10012-1 and ANSI/NCSL Z540-1. Uncertainties have been estimated at a 95% confidence level (K=2). Environmental controls are monitored to maintain 68 degree F and 50% maximum humidity. When necessary we offer ISO 17025, A2LA Calibrations through our 3rd party laboratories.