Spi 29-521-2 Class Zz Plus Plug Gage 0.521 in Dia

Product Description

The SPI 29-521-2 is a Class ZZ Plus plug gage used to verify the dimensional accuracy of machined holes and bores with a nominal diameter of 0.521 inches. Class ZZ is the standard tolerance grade for general-purpose inspection of production parts, and the Plus designation indicates the gage is manufactured to a tolerance of 0.0002 inches above the nominal size. The gage is constructed from steel, providing the hardness and wear resistance required for repeated use in shop-floor inspection work. Machinists, quality technicians, and tool room professionals use plug gages to perform fast, reliable go or no-go checks without the need for calipers or micrometers.

This plug gage is suited for general-purpose dimensional inspection in manufacturing, job shop, and production environments. It is used to check drilled, reamed, or bored holes where tight dimensional tolerances must be confirmed before assembly or further machining. The 0.521-inch diameter makes it appropriate for medium-bore inspection tasks common in mechanical component production. It is a single-end gage and is typically handled directly or mounted in a gage handle for ergonomic use during high-volume inspection.

Key Features

• Nominal diameter of 0.521 inches for precise bore inspection
• Class ZZ Plus tolerance grade at 0.0002 inches above nominal
• Steel construction for hardness and long service life
• Compact and lightweight at 0.2 pounds for easy single-hand use
• Suitable for go or no-go inspection workflows on production parts

Compatibility

Designed as a direct-fit replacement or new addition for Class ZZ plug gage sets and standard gage handle systems accepting 0.521-inch diameter plug gage blanks.

Installation Notes

Plug gages are used by quality control technicians and machinists and require no installation in the traditional sense, but proper handling practices apply. Always clean the gage and the bore being checked before use to prevent debris from affecting readings or causing premature wear. Store the gage in a protective case away from other metal tools to avoid surface damage. Calibration against a known reference standard should be performed periodically to confirm gage accuracy over time.