Spi 21-228-2 Radius Contact Point Dial Indicator

Product Description

The SPI 21-228-2 is a radius-style contact point replacement for dial indicators, machined from black oxide steel for durability and corrosion resistance. It features a 4-48 thread for secure attachment and a 1/8-inch contact point length with a 3/16-inch spherical radius tip. This contact point is used by machinists, metrology technicians, and tool-and-die professionals who need precise surface contact geometry when taking measurements with AGD Group 1 dial indicators. The black oxide finish reduces light reflection at the tip and provides mild surface protection in shop environments.

This contact point is designed for use with standard dial indicators in precision measurement applications. It is well suited for surface, bore, and runout measurements where a radius tip is preferred over a flat or pointed contact to minimize surface marking and ensure repeatable single-point contact. The 4-48 thread is the standard thread specification for AGD Group 1 dial indicator contact points, making this a common replacement or spare for gauge sets used on surface plates, magnetic bases, and fixtures in machine shops and quality control environments.

Key Features

• Radius contact tip geometry for consistent single-point contact on curved and flat surfaces
• Black oxide steel construction for durability and reduced reflectivity
• 4-48 thread fits AGD Group 1 dial indicators
• 1/8-inch contact point length for compact reach
• 3/16-inch diameter tip for stable contact geometry

Compatibility

Designed for use with AGD Group 1 dial indicators accepting a 4-48 threaded contact point. Verify thread specification on the dial indicator spindle before installation.

Installation Notes

Contact points are installed and removed by hand or with a contact point wrench — do not use pliers or tools that may damage the spindle threads. Ensure the dial indicator is not under spring load pressure before threading in the new contact point. Snug finger-tight plus a minimal tool turn is sufficient — overtightening can damage the 4-48 threads on the indicator spindle. Always verify tip engagement and zeroing procedure before taking measurements.