Spi 29-318-3 Class Zz Plus Plug Gage 0.318 in Steel

Product Description

The SPI 29-318-3 is a Class ZZ Plus plug gage designed to verify the diameter of machined holes and bores to a high degree of precision. Built from steel, this go/no-go style inspection tool checks whether a 0.318-inch diameter feature meets dimensional tolerance requirements. The gage holds a tolerance of 0.0002 inches, making it suitable for quality control checks in production and inspection environments. Machinists, toolmakers, and quality technicians use plug gages like this one as part of standard in-process and final inspection routines.

This gage is used in manufacturing and machine shop environments where hole diameter verification is required at or near 0.318 inches. It is appropriate for checking drilled, reamed, or bored holes in metal, plastic, or composite workpieces. Typical applications include incoming inspection, in-process checks on CNC-machined parts, and final acceptance inspection before assembly. It is particularly useful in shops that require traceable dimensional verification without the use of powered measurement equipment.

Key Features

• Class ZZ Plus tolerance grade for reliable go/no-go hole inspection
• 0.318-inch measurement diameter for precise hole checking
• 0.0002-inch tolerance for accurate dimensional verification
• Steel construction for durability in production environments
• Compact and lightweight at 0.2 pounds for easy handling at the machine or inspection bench

Compatibility

Designed for use as a Class ZZ Plus plug gage in standard hole inspection applications requiring a 0.318-inch nominal diameter check.

Installation Notes

Plug gages are handled and used by machinists and quality inspection personnel — no installation in the traditional sense is required. Store the gage in a protective case or designated gage block area to prevent damage to the precision ground surfaces. Clean both the gage and the part bore before use to avoid false readings caused by chips or debris. Follow your facility's gage calibration and handling procedures to maintain measurement accuracy over time.