Osg 2985901 Spiral Flute Tap 5/16-24 Unf Bottoming Hss

Product Description

The OSG 2985901 is a spiral flute bottoming tap designed for cutting internal threads in blind holes where full thread depth close to the bottom is required. Built from high-speed steel with a steam oxide coating, this tap handles 5/16-24 UNF right-hand threads and runs a 3-flute, 50-degree helix configuration that efficiently evacuates chips upward out of the hole. The 2B class of fit delivers a standard tolerance suitable for most fastener applications. Overall length is 2.719 inches, making it a compact, purpose-built threading tool for production and repair work performed by machinists and maintenance trades.

This tap is suited for threading aluminum and carbon steel workpieces in both shop and field maintenance environments. The bottoming chamfer style allows threads to be cut within a few pitches of a blind hole bottom, making it the correct choice when a plug or taper tap cannot reach full thread depth. It is used in manual tapping, tapping fixtures, and low-speed CNC or drill press setups where the short chamfer lead is appropriate.

Key Features

• Bottoming chamfer for threading close to the bottom of blind holes
• 50-degree right-hand spiral flute helix for upward chip evacuation
• High-speed steel construction for durability across aluminum and carbon steel
• Steam oxide coating reduces friction and improves lubrication retention
• 2B class of fit for standard tolerance internal thread applications
• No coolant-through design — suitable for hand tapping and standard machine tapping

Compatibility

Designed as a standard 5/16-24 UNF bottoming tap compatible with workpieces in aluminum and carbon steel; fits standard tap holders and chucks sized for a 0.318-inch shank diameter.

Installation Notes

This tap should be installed by a qualified machinist or maintenance technician using an appropriate tap wrench, tapping fixture, or machine spindle. Always secure the workpiece firmly and use a suitable cutting fluid or tapping compound for the base material before threading. Back the tap out periodically to clear chips and prevent breakage, particularly in deep blind holes. Inspect the tap for wear or chipping before each use and replace if thread quality degrades.