Thread Gauges

Gauges for Internal Threads

Use of internal thread GO gauge

An internal thread GO gauge checks the theoretical size of the internal thread (measurement of the theoretical pitch diameter). (Thread Tables) This is achieved by checking the minimum limit of the pitch diameter, taking into account pitch errors, errors in the flank angles, and form deviations, which cause an apparent reduction of the pitch diameter of the workpiece (theoretical pitch diameter). In addition, it checks the minimum limit of the major diameter and also whether the length of the straight flank is sufficient, i.e. that the rounding at the root of the profile does not interfere excessively with the thread flank. This measuring instrument does not check the minor diameter of the workpiece thread. The GO thread gauge, when screwed in by hand without using excessive force, enters along the full length of the thread of the workpiece to be checked. If entry is not possible, the workpiece thread does not meet the specifications.

Use of internal thread NOGO gauge (with red marking)

An internal thread NOGO gauge checks whether the actual pitch diameter exceeds the specified maximum size.

The internal thread NOGO gauge, when screwed in by hand without using excessive force, can enter from both ends of the tapped section, but not more than two thread turns. If it can be screwed in more than two turns, the thread does not meet the specifications.

External Thread Gauges

Use of external thread gauge with GO rings

An external thread GO gauge checks the virtual size of the external thread (measurement of the theoretical pitch diameter), i.e. it checks the maximum material limit of the pitch diameter, taking into account deviations due to form and pitch errors and errors in the flank angles, which produce an apparent increase of the pitch diameter of the workpiece. It also checks that the maximum minor diameter has not been exceeded. The major diameter of the external thread is not checked by this gauge. The GO thread ring gauge, when screwed on by hand without using excessive force, must pass along the full length of the thread of the workpiece. If assembly is not possible, the workpiece thread does not meet the specifications.

Use of external thread NOGO gauge (with red marking)

An external thread NOGO gauge is intended to check whether the actual pitch diameter of a workpiece to be machined exceeds the specified minimum size. An external thread NOGO gauge, when screwed onto the workpiece thread by hand without using excessive force, can enter from both sides but not more than two thread turns. If the gauge can be screwed onto the workpiece by more than two turns, the thread does not comply with the specifications.

Internal thread inspection

Minimum-size workpiece

The thread gauge can be screwed in (into or onto) until the minimum step of the thread gauge is reached.

The workpiece thread is at the minimum size.

Workpiece within tolerances

The thread gauge can be screwed in (into or onto) between the minimum and the maximum step of the thread gauge.

The workpiece thread is within tolerance.

Maximum-size workpiece

The thread gauge can be screwed in (into or onto) until the maximum step of the thread gauge is reached. The workpiece pitch is at the maximum size.

Workpiece smaller than tolerance

The GO / NOGO thread gauge cannot be screwed in until the minimum step is reached. The GO / NOGO thread gauge cannot be screwed past the minimum step.

The workpiece thread is smaller than tolerance.

Workpiece larger than tolerance

The GO / NOGO thread gauge cannot be screwed past the maximum step. The GO / NOGO thread gauge cannot be screwed in until the maximum step is reached. The workpiece thread is oversized.