Thread ring gauges for external threads
Thread ring gauges check external threads on bolts, screws, shafts and pipes. VÖLKEL makes more than 800 precision ring gauges as go ring gauges and no-go ring gauges to DIN ISO 1502 for metric coarse and fine threads, to ANSI B1.2 for UNC and UNF, to DIN EN ISO 228-2 for pipe threads G and for tapered NPT threads. The standard tolerance is 6g, alongside 6e for threads with more clearance and 2A for UN threads.
Go and no-go ring gauges belong together
Unlike the plug gauge, the two ends are separate tools. The go ring gauge must screw on over the full thread length, otherwise the external thread is too large or the profile incomplete. The no-go ring gauge, recognisable by its red marking, may screw on at most two turns, otherwise the thread is too small. Only both results together give a valid verdict.
Choosing the tolerance
Metric external threads are usually made and checked in 6g. 6e applies to threads with more clearance, for example before a thicker coating. UN threads are checked with 2A, pipe threads G to DIN EN ISO 228-2 with class A. The gauge must match the tolerance of the die the thread was made with.
Checking and care
The thread should be clean, deburred and free of chips, and the gauge guided without force and without tools. Ring gauges are precision parts; oil lightly after use and store separately. For internal threads see the matching plug gauges, for external threads made with a die the matching round dies. Basics of thread inspection are in Checking threads with gauges.
