Spi 34-378-0 Plug Thread Gage 1/4-28 3B Double End

Product Description

The SPI 34-378-0 is a double-end plug thread gage designed to inspect 1/4-28 UNF internal threads to 3B class tolerance. One end carries the Go member; the opposite end carries the No Go member. A handle is included. The gage is manufactured from steel and ships with a traceability certification traceable to NIST standards, making it suitable for quality-control documentation in precision manufacturing, maintenance shops, and inspection departments. Machinists, QC inspectors, and tool-room technicians use this type of gage to verify that tapped holes fall within the accepted tolerance range before assembly.

This gage is used wherever 1/4-28 fine-pitch internal threads must be verified against 3B class limits. Typical applications include incoming inspection of threaded components, in-process verification on manual or CNC machining operations, and final inspection before shipment. The double-end configuration eliminates the need to handle a separate Go and No Go gage, speeding up high-volume inspection routines. The included handle is size 1, appropriate for this thread diameter range.

Key Features

• Go and No Go members on a single double-end gage body for efficient inspection
• Inspects 1/4-28 UNF internal threads to 3B class tolerance
• Steel construction for durability in shop environments
• NIST-traceable certification included for quality documentation and calibration records
• Size 1 handle included — no separate handle purchase required

Compatibility

Designed for inspection of 1/4-28 UNF internal threads manufactured to 3B class tolerance per applicable thread standards.

Installation Notes

This gage is a hand inspection tool and does not require installation. Clean the threaded hole and gage members before use to prevent debris from affecting readings. Apply the Go member by hand torque only — never force or use a wrench, as this can damage gage members or give false readings. Store in a protective case when not in use to preserve calibration integrity.