Thread lead is the distance between threads, measured on a plane parallel to the threaded part. Lead gages inspect the distance between thread grooves on a threaded part. These gages will inspect both internal and external thread lead using contact points that seat in the threads of the part. The pitch of the thread determines the diameter of the contact points required for taking measurements.

The LG-5002 uses a two-point system to inspect thread lead for ACME, Stub ACME, UN or API threads. The two points allow for a sweeping action to obtain the measurement.

The LG-5003 uses a three point system to inspect thread lead for ACME, Stub ACME, UN or API threads. Two fixed points at the rear of the gage and one movable contact point at the front of the gage provide complete stability when taking thread lead measurements. This unique design does not require sweeping to obtain measurements. Plus, contact points are easily relocated or changed to allow the gage to be used on a variety of thread forms.

Before inspecting parts, the lead gage must be preset to a nominal predetermined dimension using a lead gage setting standard. These setting standards are manufactured according to ANSI and API specifications. Lead standards are available for ACME, Stub ACME, UN and API threads.