The JBO Thread Plug Gauge is a go/no-go inspection tool built for metric coarse threads. It helps machinists, engineers, and quality teams quickly confirm that threaded holes meet the correct size for M39 x 4 fasteners, ensuring reliable assembly every time.

This right-hand gauge is crafted from hardened steel for durability in busy workshop environments. Its go/no-go design delivers fast, decisive pass/fail checks, reducing inspection time and helping you keep production moving with confidence.

• Go/No-Go design for fast verification: Quickly confirm hole acceptance by verifying that the go end fits within tolerance while the no-go end does not, enabling rapid decisions and reducing downtime.
• Designed for metric coarse threads (M39 x 4, 6H): Ensures consistent, repeatable checks for the correct thread size and tolerance, improving assembly reliability.
• Hardened steel construction: Built to withstand daily shop use and maintain accuracy over time, delivering long-lasting performance even in demanding environments.

Using this gauge, you’ll speed up quality checks, minimize guesswork, and improve the reliability of threaded assemblies. The robust construction and precise go/no-go feedback help you identify out-of-tolerance holes early, reduce rework, and keep your manufacturing or maintenance workflow on track—from inspection to final assembly.