Osg 1293501 Extension Tap 5/16-18 Spiral Point Hss

Product Description

The OSG 1293501 is a spiral point plug extension tap designed for threading operations in metal fabrication and machining applications. Built from high-speed steel with a steam oxide finish, this tap handles right-hand threading in a 5/16-18 UNC thread form at an H3 thread limit. It measures 4 inches in overall length with a 1-1/8 inch thread length, making it well suited for reaching into recessed or deep holes where a standard-length tap would fall short. The plug chamfer style distributes cutting load across several leading threads, which reduces torque demand and helps maintain thread accuracy. The 3-flute spiral point design pushes chips forward ahead of the cutting zone, keeping flutes clear in through-hole applications.

This tap is intended for use in cast iron, aluminum castings, aluminum, and carbon steel. It fits threading operations in production machining, tool and die work, maintenance and repair, and general metalworking environments. The reduced shank and extended neck length of 1.263 inches allow clearance when working in deep bores or past obstructing features. The 3B class of fit produces standard commercial-tolerance internal threads compatible with 3A-class fasteners. It is sold individually and is appropriate for hand tapping or use in CNC and manual machine tapping operations.

Key Features

• 5/16-18 UNC right-hand thread form at H3 thread limit for controlled tolerance threading
• Spiral point design pushes chips forward, ideal for through-hole applications
• High-speed steel construction provides durability across cast iron, aluminum, and carbon steel
• Steam oxide finish improves lubricity and reduces galling during cutting
• Extended overall length of 4 inches with reduced shank for deep-reach access
• Plug chamfer distributes entry load across multiple threads for smoother starts

Compatibility

Designed for threading 5/16-18 UNC through-holes in cast iron, aluminum castings, aluminum, and carbon steel workpieces. Produces 3B class internal threads compatible with standard 3A-class 5/16-18 fasteners.

Installation Notes

Installation is performed by machinists or maintenance technicians using a tap wrench, tapping head, or CNC tapping cycle. Ensure the workpiece is securely fixtured and the tap is properly aligned to the drilled hole before engagement to prevent tap breakage. Use appropriate cutting fluid for the workpiece material to extend tool life and improve thread finish. Follow ANSI B94.9 standards for tap drill sizes and apply consistent feed pressure to avoid overloading the flutes.