Osg 0146301 Spiral Flute Sti Tap 1/4-28 Unf Vanadium Hss

Product Description

The OSG 0146301 is a spiral flute STI (Screw Thread Insert) tap designed for cutting internal threads that accept Heli-Coil and similar threaded inserts. Ground from vanadium high-speed steel (HSS) with a steam oxide finish, it runs at the H3 thread limit for consistent tolerancing in production and repair work. The 45-degree helix angle pulls chips up and out of the hole, making this tap well suited for blind-hole applications where chip evacuation is critical. The bottoming chamfer reaches close to the bottom of a drilled hole with minimal thread lead-in. Overall length is 2.5 inches with a 0.255-inch shank diameter and 1-inch thread length.

This tap is used in maintenance, repair, and manufacturing environments where damaged or stripped threads need to be reconditioned using threaded inserts. The 1/4-28 UNF thread form targets fine-thread fastener applications common in automotive, aerospace, and precision mechanical assemblies. It is appropriate for use in carbon steel, hardened steel, and stainless steel workpieces as specified by the manufacturer. The right-hand flute direction is standard for conventional right-hand thread cutting.

Key Features

• 45-degree helix angle drives chips upward for reliable chip evacuation in blind holes
• Bottoming chamfer style allows threading to within a few pitches of hole bottom
• Vanadium high-speed steel construction provides wear resistance across carbon, hardened, and stainless steels
• Steam oxide finish reduces friction and improves lubrication retention during cutting
• H3 thread limit ensures consistent fit for STI insert installation
• Right-hand cut, 3-flute design for balanced cutting action

Compatibility

Designed for cutting oversized STI threads in 1/4-28 UNF applications to accept standard Heli-Coil style threaded inserts. Rated for use in carbon steel, hardened steel, and stainless steel per manufacturer material application data.

Installation Notes

Installation is performed by machinists or maintenance technicians using a standard tap wrench, T-handle, or machine tapping setup. The workpiece must be drilled to the correct STI tap drill diameter before tapping - consult the insert manufacturer drill chart for the specific insert series being used. Apply appropriate cutting fluid for the workpiece material, especially when working in stainless steel. Secure the workpiece fully before starting and avoid reversing the tap while chips are packed in the flutes.