Starrett 68131 Inside Micrometer 0.375-0.500 Inch Range

Product Description

The STARRETT 68131 is a mechanical inside micrometer designed for precise internal bore and hole measurements in the 0.3750 to 0.5000 inch range. It uses three self-centering contact points with solid carbide measuring faces to deliver consistent, true readings without operator-induced alignment error. Graduation is 0.0003 inches with an accuracy of 0.000150 inches, making it suitable for close-tolerance work in machining, maintenance, and precision assembly. The ratchet stop thimble ensures repeatable measuring pressure, which is essential when working to tight tolerances on valve bores, cylinder sleeves, bearing housings, and similar applications.

This inside micrometer is used in machine shops, industrial maintenance, and precision trades where accurate internal measurement of small bores is required. The 0.3750 to 0.5000 inch range targets smaller-diameter bores common in hydraulic fittings, pump housings, and mechanical assemblies. A maximum extension rod length of 6.0000 inches and a gage depth of 2.25 inches allow measurement in moderately deep bores. The instrument ships complete with a case, contacts, setting ring, wrenches, and instructions, making it ready for immediate use on arrival.

Key Features

• Three self-centering contacts automatically align to the bore centerline for true, repeatable readings
• Solid carbide measuring faces resist wear on hardened or abrasive surfaces
• Ratchet stop thimble maintains consistent measuring pressure to protect accuracy
• Graduation of 0.0003 inches and accuracy of 0.000150 inches for close-tolerance applications
• Setting ring included for field calibration verification without returning to a standards lab
• Maximum extension rod length of 6.0000 inches covers moderately deep bore access

Compatibility

Designed as an OEM-style precision measuring instrument for use across machining, industrial maintenance, and mechanical assembly applications requiring internal measurement of bores in the 0.3750 to 0.5000 inch range.

Installation Notes

Inside micrometers are precision instruments and should be handled by qualified machinists or technicians familiar with bore gauging procedures. Verify calibration against the included setting ring before use and after any impact or temperature change. Keep the instrument clean and lightly oiled per manufacturer instructions; store in the provided case when not in use. Do not force the thimble past its measurement range, as this can damage the spindle or contacts.