Osg 1303900700 Spiral Flute Sti Tap 1/4-28 Unf Hss

Product Description

The OSG 1303900700 is a spiral flute STI (Screw Thread Insert) tap designed for cutting threads that accept helical wire inserts in aluminum and similar materials. It features a 1/4-28 UNF thread form, a 50-degree right-hand helix, and a semi-bottoming chamfer that allows threading close to the bottom of a blind hole. Manufactured from high-speed steel with a bright finish, this tap carries an H3 thread limit and a 2B class of fit. The three-flute configuration promotes chip evacuation in through-hole and semi-blind applications. Overall length is 2-23/32 inches with a shank diameter of 0.318 inches.

This tap is suited for machining and repair operations where STI inserts are required to restore or reinforce threaded holes. Typical applications include aerospace, automotive, and general manufacturing environments where aluminum components require durable, insert-ready threads. The semi-bottoming chamfer makes it practical for blind-hole work while still allowing flexibility in through-hole setups. It is used by machinists, maintenance technicians, and toolroom professionals working to Series 13039 specifications.

Key Features

• 1/4-28 UNF thread form for fine-pitch STI insert preparation
• 50-degree right-hand spiral flute promotes efficient chip evacuation
• Semi-bottoming chamfer allows threading near the base of blind holes
• H3 thread limit with 2B class of fit for consistent insert fitment
• High-speed steel construction for durability across general-purpose cutting
• Bright finish with no coating — suitable for use with cutting fluids

Compatibility

Designed for use in aluminum and similar materials requiring STI threaded inserts. Compatible with standard 1/4-28 UNF helical wire insert systems.

Installation Notes

This tap is installed by machinists using standard tapping equipment with appropriate cutting fluid for aluminum. Always ensure the workpiece is secured and the tap is properly aligned before engagement to avoid tap breakage. Follow the tool manufacturer and shop safety guidelines when handling cutting tools. Inspect the tap for wear or damage before each use and replace if thread form degradation is observed.