Cleveland C91721 Solid Pilot Counterbore 3/4 in Hss

Product Description

The CLEVELAND C91721 is a solid pilot counterbore designed for precision spot-facing and counterboring operations in ferrous metals. Built from high-speed steel with a bright, uncoated finish, it features a 3/4 inch (0.7500 inch decimal) counterbore diameter and a 1/2 inch straight-cylindrical shank. The 3-flute geometry provides stable, chatter-resistant cutting in forward direction. With an overall length of 7.25 inches, this tool suits standard drill press and milling machine setups. Machinists and tool-and-die tradespeople rely on this style of counterbore for creating accurate recessed seat diameters around drilled holes in production and maintenance environments.

The C91721 is sized to accommodate 1/2 inch socket-head cap screws, making it a go-to tool for mechanical assembly work where cap screw heads must sit flush or below the workpiece surface. It is well-suited for use in carbon steel, alloy tool steel, and cast iron — common materials in industrial fabrication, machine repair, and fixture building. The standard pilot diameter of 0.5000 inches (12.70 mm) self-locates in a pre-drilled clearance hole, keeping the counterbore concentric without the need for a separate guide bushing.

Key Features

• 3/4 inch (19.05 mm) counterbore diameter seats 1/2 inch socket-head cap screws
• High-speed steel construction handles alloy tool steel, carbon steel, and cast iron
• 3-flute design promotes smooth, stable cutting and efficient chip evacuation
• Standard 1/2 inch straight-cylindrical shank fits common drill press and mill chucks
• Bright, uncoated finish — no coating buildup concerns on tight-tolerance seats
• 7.25 inch overall length provides clearance for deep-reach counterboring setups

Compatibility

Designed for use with 1/2 inch socket-head cap screws. Suitable for counterboring carbon steel, alloy tool steel, and cast iron workpieces on drill presses, knee mills, and machining centers with a compatible 1/2 inch chuck or collet.

Installation Notes

This tool is installed and operated by machinists or skilled tradespeople using standard drill press or milling machine setups. Always secure the workpiece firmly before engaging the cutter, and ensure the pilot diameter matches the pre-drilled hole before use. Operate at appropriate spindle speeds for high-speed steel tooling in the material being cut — consult published HSS cutting-speed charts for the specific workpiece material. Apply cutting fluid when counterboring steel or cast iron to extend tool life and improve finish quality.