Spi 34-351-7 Plug Thread Gage 4-40 2B Double End

Product Description

The SPI 34-351-7 is a double-end plug thread gage used to verify internal thread quality on 4-40 UNC tapped holes to a 2B class-of-fit standard. One end is the Go member, which confirms the thread form and pitch diameter fall within the low-limit tolerance. The opposite end is the No Go member, which confirms the pitch diameter does not exceed the high-limit tolerance. A handle is included. The gage is manufactured from steel and ships with a NIST traceability certification, making it suitable for use in quality-control and inspection environments where documented calibration traceability is required.

This gage is used in machine shops, manufacturing facilities, and maintenance environments wherever 4-40 UNC tapped holes must be inspected for conformance. Typical applications include production inspection of threaded fastener holes in sheet metal, electronic enclosures, instrument panels, and precision assemblies. The double-end design speeds up the Go and No Go check without requiring the inspector to swap gage members or handles.

Key Features

• Double-end design provides both Go and No Go members in a single tool
• Checks 4-40 UNC internal threads to 2B class-of-fit tolerance
• Steel construction for durability and dimensional stability
• NIST traceability certification included for quality-system compliance
• Handle included — no separate handle purchase required

Compatibility

Designed for inspection of 4-40 UNC tapped holes conforming to 2B class-of-fit requirements per NIST standards.

Installation Notes

Thread gages are inspection tools, not cutting tools — never force the Go or No Go member into a tapped hole. The Go end should pass through the full thread length under hand pressure only; the No Go end should not enter more than two turns. Store the gage in its case when not in use to prevent nicks or corrosion that would affect gage accuracy. Periodic re-calibration against traceable standards is recommended to maintain inspection integrity.