Osg 2493803 Straight Flute Tap 5/16-18 Unc Bottoming

Product Description

The OSG 2493803 is a straight flute machine tap designed to cut 5/16-18 UNC internal threads in bottoming applications. It features four flutes ground from vanadium high-speed steel and finished with a nitride coating for improved wear resistance and surface hardness. With a 2B class of fit and H5 thread limit, this tap produces threads to standard tolerance for general mechanical assemblies. The overall length is 2-23/32 inches with a thread length of 1-1/8 inches, making it well suited for blind holes where full thread depth is needed close to the bottom. Licensed machinists and maintenance technicians are the primary users.

This tap is intended for machine tapping operations in materials including aluminum and cast iron. The bottoming chamfer — typically 1 to 2 threads of lead — allows threading to near the bottom of a blind hole, a common requirement in close-tolerance fixture and component work. It is part of OSG Series 240 and is suited for use in CNC machining centers, drill presses, and tapping machines where controlled feed and speed are maintained. Coolant-through capability is not included, so external coolant or cutting fluid application is recommended when tapping harder materials.

Key Features

• Bottoming chamfer for threading to the bottom of blind holes
• Vanadium high-speed steel construction for toughness and edge retention
• Nitride coating increases surface hardness and reduces built-up edge
• 4 flutes with right-hand thread direction, H5 thread limit, 2B class of fit
• Rated for aluminum and cast iron applications
• Part of OSG Series 240 machine tap line

Compatibility

Designed as a standard 5/16-18 UNC bottoming machine tap for use in CNC machining centers, drill presses, and tapping machines that accept straight shank taps with a 0.318-inch shank diameter.

Installation Notes

Installation is performed by machinists or maintenance technicians using a tapping head, CNC rigid tap cycle, or hand tap wrench. The workpiece must be securely fixtured before tapping begins. A properly sized drill hole — matching the 5/16-18 UNC tap drill specification — must be prepared before use. Apply cutting fluid or tapping compound appropriate for the workpiece material to extend tool life and improve thread quality.