Spi 34-251-9 No Go Plug Thread Gage 1/4-20 6H

Product Description

The SPI 34-251-9 is a single-end No Go plug thread gage designed to verify that internally threaded workpieces do not exceed the maximum material condition for a 1/4-20 thread form. Manufactured from steel and classified to the 6H tolerance class, this gage is used in quality control and inspection environments where threaded hole conformance must be confirmed before assembly. A No Go gage should not enter a correctly cut thread — if it does, the thread is out of tolerance. The handle is sold separately and accepts a Size 1 handle. NIST traceability certification is included, supporting documented inspection processes.

This gage is suited for use in machine shops, manufacturing facilities, and any inspection environment where 1/4-20 UNC threaded holes must meet ANSI standards. Typical applications include incoming inspection of machined parts, in-process thread verification on production lines, and final inspection before assembly. The NIST-traceable certification makes it appropriate for use in ISO-compliant or regulated inspection workflows. A licensed inspector or quality technician typically performs the gauging operation.

Key Features

• No Go plug design checks that threaded holes do not exceed maximum material condition for 1/4-20 threads
• 6H tolerance classification per ANSI standards ensures accurate thread fit verification
• Steel construction provides durability for repeated use in production inspection environments
• NIST traceability certification included for use in documented or regulated inspection programs
• Single-end configuration with Size 1 handle interface (handle not included)

Compatibility

Designed for use with 1/4-20 UNC internally threaded workpieces conforming to ANSI and 6H classification standards. Accepts a standard Size 1 thread gage handle, available separately.

Installation Notes

Thread plug gages are used by quality control technicians and machinists — no power tools or utility shutoffs are required for gauging operations. Handle the gage with clean, dry hands or lint-free gloves to prevent corrosion from skin oils. Do not force the No Go member into a threaded hole; it should not enter a conforming thread. Store the gage in its protective case when not in use to preserve the calibrated thread form.