Spi 30-428-7 Small Hole Gage 0.3 to 0.4 Inch Half Ball

Product Description

The SPI 30-428-7 is a small hole gage designed for precision inside measurement of bores, holes, and slots in the 0.3 to 0.4 inch range. The half ball contact style allows the gage to seat cleanly inside a drilled or reamed hole, giving the technician a consistent feel when expanding the contact to the bore wall. Overall length is 3 inches, with a gage depth of 1.6 inches. The satin chrome finish reduces glare and resists corrosion during regular shop use. Machinists, toolmakers, and maintenance technicians use this type of gage in conjunction with an outside micrometer to transfer and record bore dimensions accurately.

This small hole gage is suited for shop floor and maintenance applications where small-bore dimensional verification is required. Typical uses include checking drilled holes, pin bores, valve guides, and similar features on both production and repair work. The compact 3 inch overall length makes it easy to maneuver in tight setups. It is appropriate for both light industrial and precision machining environments where hand tools are the standard method of bore measurement.

Key Features

• Measurement range of 0.3 to 0.4 inches for small bore applications
• Half ball contact style provides consistent, repeatable seating inside the bore
• 1.6 inch gage depth reaches into typical drilled and reamed holes
• 3 inch overall length for easy single-hand operation
• Satin chrome finish minimizes glare and provides corrosion resistance

Compatibility

Designed as a standard small hole gage for use with outside micrometers or other transfer-measuring instruments to determine inside bore dimensions in the 0.3 to 0.4 inch range.

Installation Notes

Small hole gages are hand tools that require no installation. Before use, ensure the bore being measured is clean and free of chips or burrs that could affect contact seating. Expand the gage gently inside the bore until light drag is felt, then withdraw and measure across the contact with a calibrated outside micrometer. Avoid overtightening the knurled adjusting knob, as this can distort the contact and affect reading accuracy.