The JBO Thread Plug Gauge is a precision inspection tool designed for metric fine threads. This left-hand gauge is sized M39 x 3 with 6H tolerance, making it ideal for checking threaded holes in machine shops, assemblies, and maintenance tasks.

Its knurled grip provides secure handling for comfortable use in busy environments.

• Go/No-Go design for fast pass/fail checks: Quickly verify that a hole meets both minimum and maximum thread limits, reducing inspection time and rework.
• Durable hardened steel construction: Resists wear and keeps accuracy over many uses in demanding shop environments.
• Precise left-hand metric fine thread sizing (M39 x 3, 6H): Provides consistent results for critical assemblies that require exact thread engagement.

Using this gauge helps streamline quality control, shorten setup times, and improve the reliability of threaded connections. The robust hardened steel body and precise sizing deliver dependable performance across daily tasks, from routine maintenance to high-precision manufacturing, giving you confidence with every measurement.