Spi 21-914-7 Mechanical Hole Micrometer 3.5-4 in

Product Description

The SPI 21-914-7 is a mechanical inside hole micrometer designed for precise internal bore measurement in the 3.5 to 4 inch range. It uses three self-centering contact points to align automatically within the bore, delivering consistent readings without operator-induced tilt error. Graduation is 0.0002 inches with a stated accuracy of 0.0002 inches. The chrome-finished spindle and ratchet stop thimble deliver controlled measuring pressure on every reading. Carbide measuring surfaces resist wear during repeated use in shop environments. A NIST traceability certification is included. Machinists, metrology technicians, and precision maintenance trades rely on this tool for bearing seat, cylinder, and housing inspection work.

This micrometer is suited for internal diameter measurement in manufacturing, maintenance, and quality-control applications. Typical use cases include checking machined bores, hydraulic cylinder walls, pump housings, and valve bodies where tight tolerances must be verified. The 3.5 to 4 inch measuring range covers a common bore size found in industrial and heavy-equipment components. One extension rod is included to extend reach, and a 3.5 inch setting ring is provided for zeroing the instrument before use.

Key Features

• 3.5 to 4 inch measuring range with 0.0002 inch graduation and 0.0002 inch accuracy
• Three self-centering contact points for consistent bore alignment without manual adjustment
• Carbide measuring surfaces for extended wear resistance in production environments
• Ratchet stop thimble provides repeatable, controlled measuring pressure
• NIST traceability certification included for calibration documentation requirements
• Chrome finish on body; includes one extension rod and one 3.5 inch setting ring

Compatibility

Designed as a direct-use inside hole micrometer for any bore or internal diameter application falling within the 3.5 to 4 inch measurement range.

Installation Notes

This is a precision measuring instrument, not an installed component. Handle with care to avoid dropping or impacting the contact points and carbide surfaces. Zero the micrometer against the included setting ring before each measurement session. Store in the provided case away from temperature extremes and cutting fluids to maintain calibration integrity.