Spi 34-381-4 Plug Thread Gage 5/16-18 2B Go No Go

Product Description

The SPI 34-381-4 is a double-end plug thread gage used to verify internal threads to the 5/16-18 UNC standard at a 2B tolerance class. One end carries the Go member and the opposite end carries the No Go member, allowing a technician to confirm both minimum and maximum thread acceptance limits in a single tool. The gage body is steel construction and ships with a size 1 handle included. A NIST-traceable calibration certificate is included, making this tool ready for use in quality-controlled environments without additional calibration sourcing. Machinists, quality inspectors, and tool-and-die shops rely on this type of gage for in-process and final inspection of threaded holes.

This gage is suited for inspection of 5/16-18 UNC tapped holes in production machining, MRO maintenance settings, and fabrication shops. The double-end design eliminates the need to store two separate gages for a single thread size, reducing bench clutter and the risk of misidentifying individual Go or No Go members during high-volume inspection runs. The included handle accepts standard replacement gage members when wear eventually requires it.

Key Features

• Double-end configuration with Go and No Go members on a single handle
• Verifies 5/16-18 UNC internal threads to 2B tolerance class
• Steel construction for durability in production and inspection environments
• Size 1 handle included — no separate handle purchase required
• NIST-traceable traceability certificate included for quality-system compliance

Compatibility

Designed for inspection of 5/16-18 UNC tapped holes held to a 2B tolerance class per applicable thread standards.

Installation Notes

Thread plug gages are installed and used by quality technicians, machinists, or inspection personnel — not by installation trades. Before use, clean the threaded hole of chips, coolant, and debris to avoid false rejects or gage wear. The Go member should pass through the full thread engagement length under hand pressure only; never force a plug gage with tools. Store the gage in a protective case away from other metal tooling to prevent damage to the precision ground thread members.