Osg 2985800 Spiral Flute Tap 5/16-18 Unc Bottoming Hss

Product Description

The OSG 2985800 is a spiral flute bottoming tap designed to cut internal 5/16-18 UNC right-hand threads in blind holes where full thread depth close to the bottom is required. Manufactured from high-speed steel with a bright uncoated finish, it features three flutes wound at a 50-degree helix angle. That steep helix efficiently evacuates chips upward out of the hole, reducing clogging in ductile materials. The 2B class of fit produces a standard tolerance thread suitable for most general-assembly applications. Overall length is 2.719 inches with a shank diameter of 0.318 inches. Licensed machinists, tool-and-die makers, and maintenance mechanics are the primary users.

This tap is suited for threading aluminum and carbon steel workpieces in both production and maintenance-repair environments. The bottoming chamfer — typically 1 to 2 threads of lead — allows threading to within a very short distance of the blind hole floor, making it the correct choice after a plug or taper tap has started the thread. It is used in manual tapping, drill press, and CNC tapping operations where the machine or operator controls feed rate carefully to match the 18 threads-per-inch pitch.

Key Features

• Bottoming chamfer for maximum thread depth in blind holes
• 50-degree right-hand spiral helix for upward chip evacuation
• High-speed steel construction for durability across aluminum and carbon steel
• Bright uncoated finish — ready for use or compatible with aftermarket coatings
• 2B class of fit for standard general-purpose thread tolerance
• No coolant-through requirement; compatible with flood, mist, or cut-paste lubrication

Compatibility

Designed to cut 5/16-18 UNC 2B right-hand internal threads in aluminum and carbon steel. Fits standard 5/16-inch tap holders and collets accepting a 0.318-inch shank diameter.

Installation Notes

This tap is installed and driven by a licensed machinist or maintenance mechanic using a tap wrench, drill press, or CNC tapping head set to the correct feed rate for 18 TPI. Always pre-drill the correct tap drill diameter before threading and clear chips frequently when hand-tapping blind holes to avoid tap breakage. Apply a suitable cutting fluid or tapping compound rated for the workpiece material before and during the operation. Never force the tap if resistance increases suddenly — back off to clear chips before continuing.