Through gauge is used to detect the minimum limit of the contact thread, which is to ensure that the metric 6g and imperial Class 2A bolts can get into the threaded holes.
    Method of application: Through gauge should be able to enter through the entire length of the thread engagement portion of the inner and outer. The best condition for gauge is that it can be free rotation in the threaded hole and have the minimum of wear. If the gauge may be through the threaded hole, but have a certain blockage, it is acceptable, but it will cause wear, and therefore it frequent needs calibration. Prohibit forced to rotate the gauge into the threaded hole by hand.

An enlarged view of the threaded portion