Spi 34-421-8 Plug Thread Gage 3/4-20 2B Double End

Product Description

The SPI 34-421-8 is a double-end plug thread gage designed to verify internal thread conformance to 3/4-20 specifications at 2B class tolerance. One end carries the Go member and the other the No Go member, allowing the technician to confirm both the minimum material condition and the maximum material condition in a single tool. The gage ships with a size 3 handle already installed. Construction is steel throughout. Traceability certification to NIST standards is included, satisfying documentation requirements in quality-controlled manufacturing and inspection environments. Machinists, quality control inspectors, and tool-crib personnel are the primary users.

This gage is suited for production inspection and incoming-goods inspection of threaded bores calling out 3/4-20 UNF thread at a 2B fit class. Typical applications include aerospace, automotive, hydraulic, and general machining shops where thread-fit documentation is required. The included NIST traceability certificate supports ISO 9001 and AS9100 quality management system recordkeeping. The double-end design reduces the number of individual gages needed at the inspection station and keeps workflow efficient on the bench or on the floor.

Key Features

• Go and No Go members on a single double-end gage body — one tool covers full 2B class thread verification
• 3/4-20 thread size with 2B class tolerance for precise fit conformance inspection
• NIST traceability certification included for quality management system compliance
• Size 3 handle included — no additional handle purchase required
• Steel construction for durability under repeated production-inspection use

Compatibility

Designed for inspection of internal 3/4-20 UNF threaded features held to ANSI 2B class tolerance. Suitable for use with standard size 3 plug gage handles.

Installation Notes

Thread plug gages are inspection instruments, not cutting tools — do not force the Go member into a non-conforming bore. Store the gage in its case when not in use to protect the thread form from nicks and corrosion. Periodic recalibration against a NIST-traceable master is recommended to maintain measurement integrity. Handle the gage with clean, dry hands or cotton gloves to prevent surface corrosion on the steel members.