The JBO Thread Plug Gauge is a purpose-built tool for checking metric fine threaded holes, specifically sized for M8 x 0.5 threads in the 4H class. With its Go/No-Go design, it provides a fast, clear yes-or-no check on whether a hole is within tolerance, helping parts assemble correctly the first time. This right-hand gauge is ideal for engineers, inspectors, machinists, and maintenance teams who need reliable thread verification without slow, guesswork-driven testing.

Made for busy shops and quality teams, this gauge uses hardened steel and precise machining to deliver durable, repeatable results you can trust project after project.

• Go/No-Go design for fast, decisive verification: One end (Go) confirms the hole meets the minimum material condition, while the No-Go end confirms it does not exceed the maximum tolerance. This simple pass/fail check speeds inspections and reduces guesswork in assembly.
• Fine-metric compatibility: M8 x 0.5 in a 4H class: Precisely matched to metric fine-thread standards, ensuring reliable checks for holes that require a tight fit and consistent thread engagement across parts.
• Hardened steel construction for long tool life: Tough, wear-resistant steel and quality machining withstand daily use in workshop environments, preserving accuracy and reducing replacement costs.

Using this gauge streamlines your threading checks, cuts inspection time, and helps prevent misfits in assemblies. Its durable construction provides confidence that measurements stay stable through repeated use, while its compact, easy-to-handle form fits into typical inspection setups and toolboxes, supporting a smoother, more efficient workflow from machining to assembly.