A Go/No-Go thread ring gauge is a two-part tool used to check external threads, where the Go gauge should thread on easily to confirm the thread is within its maximum size limits, and the No-Go gauge should not thread on more than a few turns to ensure the thread is not too loose or undersized. The Go ring gage checks the maximum minor and pitch diameters, while the No-Go ring gage checks the minimum pitch diameter.
Go ring gauge
Purpose: To verify that the thread is large enough, meaning it meets the minimum size requirements.
Usage: It should thread onto the part smoothly and completely.
Result if it doesn’t fit: The part is too large and out of specification.
No-Go ring gauge
Purpose: To verify that the thread is not too small, meaning it has not exceeded the maximum size limit for the pitch diameter.
Usage: It should not thread on more than one or two turns. If it threads on easily, the part is too large.
Result if it threads on completely: The part is undersized and out of specification.
Key takeaway
Go: Threads on; the part is not too large.
No-Go: Does not thread on completely; the part is not too loose.
A correctly manufactured thread will allow the Go gauge to thread on fully, but not the No-Go gauge.
