Spi 23-127-4 Threaded Ring Gage 4-40 Class 2A Go No Go

Product Description

The SPI 23-127-4 is a double-ring threaded ring gage used to verify external thread conformance on 4-40 UNC fasteners and threaded components. It combines Go and No Go members in a single double-ring design, allowing technicians to confirm that a threaded part meets Class 2A tolerance limits without switching tools. Made from tool steel, the gage delivers the hardness and dimensional stability required for accurate, repeatable inspection. Traceability is backed by NIST certification, making this gage suitable for quality control environments that require documented measurement standards. Machinists, quality inspectors, and precision manufacturing shops are the primary users of this type of gage.

This gage is suited for inspecting small 4-40 threaded parts in production and incoming inspection settings. The Class 2A classification covers the standard fit tolerance range used in the majority of commercial and industrial fastener applications. It is appropriate for both shop-floor use and bench inspection in aerospace, electronics, medical device, and general manufacturing environments where small-diameter thread verification is required.

Key Features

• Go and No Go members in a single double-ring gage for efficient pass/fail thread inspection
• Designed for 4-40 UNC external threads to Class 2A tolerance
• Tool steel construction for hardness and long service life
• NIST traceability certification included for documented quality control compliance
• Compact size supports benchtop and in-process inspection workflows

Compatibility

Designed for verifying external 4-40 UNC threads manufactured to Class 2A tolerance specifications in commercial and industrial applications.

Installation Notes

Threaded ring gages are used by quality inspectors and machinists and require no installation. Before use, inspect the gage and the part for burrs, chips, or contamination that could affect measurement accuracy. Apply the Go ring first — it should pass freely over the thread — then confirm the No Go ring does not fully engage. Store the gage in its protective case and calibrate on a scheduled interval to maintain measurement integrity.