Spi 34-428-3 Plug Thread Gage 7/8-20 3B Class Go No Go

Product Description

The SPI 34-428-3 is a double-end plug thread gage used to verify internal thread conformance to a 7/8-20 thread specification at a 3B tolerance class. The Go end confirms the thread will accept a mating fastener within the allowable pitch diameter range. The No Go end confirms the thread is not oversized beyond the upper tolerance limit. Both ends are machined from steel for dimensional stability and wear resistance. A size 4 handle is included. This gage is used by machinists, quality control inspectors, and toolroom technicians in production and inspection environments.

This gage applies to internal 7/8-20 Unified National Fine (UNF) threads classified to the 3B standard, which is the standard precision class for most threaded fastener applications in mechanical assemblies. It is suited for incoming inspection, in-process verification, and final acceptance checks. The double-end configuration places the Go and No Go members on opposite ends of a single handle, reducing the need for multiple tools during thread inspection routines.

Key Features

• Double-end design with Go and No Go members on a single size 4 handle
• Verifies 7/8-20 internal threads to 3B tolerance class
• Steel construction for durability and dimensional stability
• NIST traceability certification included for calibration records
• Handle included - no separate purchase required

Compatibility

Designed for inspection of internal 7/8-20 thread forms classified to the 3B standard in accordance with NIST-referenced gage standards.

Installation Notes

Thread gages are inspection instruments, not cutting or forming tools. Handle with clean, dry hands or lint-free gloves to prevent corrosion from skin contact. Store in a protective case when not in use to maintain gage accuracy. Calibration should be verified against the included NIST traceability certification prior to use in a formal inspection process.