Spi 29-491-8 Class Zz Plus Plug Gage 0.491 in

Product Description

The SPI 29-491-8 is a Class ZZ Plus plug gage used to verify the diameter of holes and bores to a nominal size of 0.491 inches. It is manufactured from steel and holds a tolerance of 0.0002 inches, making it suitable for go/no-go inspection work in machining, fabrication, and quality-control applications. Class ZZ is the standard tolerance class for general-purpose gaging, and the Plus designation indicates the gage is sized at the upper end of the tolerance range. Machinists, tooling technicians, and quality inspectors use plug gages like this to confirm feature size compliance on production and repair parts.

This gage is appropriate for use in machine shops, manufacturing facilities, and maintenance environments where hole diameter verification is part of standard inspection protocol. It is suited for inspecting drilled, reamed, or bored holes in both production and low-volume work. The compact size and steel construction make it practical for benchtop and in-process inspection tasks where dimensional accuracy at this bore size must be confirmed against print tolerances.

Key Features

• Nominal measurement diameter of 0.491 inches for direct bore inspection
• Class ZZ Plus tolerance of 0.0002 inches for general-purpose go/no-go gaging
• Steel construction for durability in shop environments
• Single-piece package, ready for immediate use
• Lightweight at 0.2 pounds for easy handling during inspection

Compatibility

Designed as a general-purpose Class ZZ Plus plug gage for inspecting holes and bores with a nominal diameter of 0.491 inches in accordance with standard plug gage tolerance classifications.

Installation Notes

Plug gages are handled and used by machinists, quality technicians, and inspection personnel — no power tools or utilities need to be shut down prior to use. Keep the gage clean and lightly oiled when not in use to prevent corrosion and maintain accuracy. Do not force the gage into an undersized hole, as this can damage the gage or alter its calibration. Periodic recalibration against a certified reference standard is recommended to ensure continued accuracy.