Osg 1766101 Spiral Flute Extension Tap 4-40 Unc H2 Vanadium Hss

Product Description

The OSG 1766101 is a spiral flute extension tap designed for threading 4-40 UNC internal threads in demanding materials including carbon steel, hardened steel, and stainless steel. Manufactured from vanadium high-speed steel and finished with a steam oxide coating, this tap provides improved lubricity and corrosion resistance during cutting operations. The modified bottoming chamfer allows threading close to the bottom of a blind hole. With a 4-inch overall length and a reduced shank, it reaches into recessed or deep workpiece features where standard-length taps cannot. The right-hand spiral flute design pulls chips up and out of the hole, making it well suited for blind-hole tapping applications in production and maintenance machining environments.

This extension tap is used in machine tapping and hand tapping operations where thread access depth or clearance is a limiting factor. Its H2 thread limit provides a controlled tolerance for achieving 2B and 3B class-of-fit threads, which cover the majority of standard inch-series fastener applications. The 30-degree helix angle and three-flute configuration balance chip evacuation with cutting efficiency across a range of work materials. Machinists, tool and die technicians, and maintenance mechanics working in job shop, production, or MRO environments will find this tap appropriate for threading operations in tight or deep access situations.

Key Features

• Spiral flute geometry with 30-degree helix angle evacuates chips from blind holes during tapping
• Modified bottoming chamfer threads to near-full depth in blind hole applications
• Vanadium high-speed steel construction supports use in carbon steel, hardened steel, and stainless steel
• Steam oxide finish improves lubricity and reduces galling during thread cutting
• 4-inch overall length with reduced shank provides extended reach into deep or recessed features
• H2 thread limit produces 2B and 3B class-of-fit threads for standard inch-series fastener compatibility

Compatibility

Designed for threading 4-40 UNC internal threads to 2B and 3B class-of-fit tolerances in carbon steel, hardened steel, and stainless steel workpieces. Suitable for use in both hand tapping and machine tapping setups where extended reach is required.

Installation Notes

This tap is installed and operated by machinists, toolmakers, or maintenance mechanics using standard tapping handles, tap wrenches, or CNC and manual machine tool spindles. Always secure the workpiece and ensure the tap is properly aligned to the pilot hole before engagement to prevent tap breakage. Use cutting fluid appropriate for the work material to extend tap life and improve thread quality. Follow applicable shop safety procedures and machine guarding requirements when tapping on powered equipment.