Osg 31400801 Spiral Point Sti Tap 1/4-20 Unc 3 Flute

Product Description

The OSG 31400801 is a spiral point STI tap designed for tapping STI (Screw Thread Insert) holes in metal workpieces. It produces the oversized internal threads required to accept helical wire inserts, restoring or upgrading thread strength in aluminum, cast iron, steel, and similar materials. Built from powdered metal with an oxide finish, this tap is suited for production and maintenance applications where consistent thread form and tool longevity matter. It features a plug chamfer, 3 flutes, H3 thread limit, and a 2B class of fit on a 1/4-20 UNC thread profile. Overall length is 2.72 inches with a thread length of 0.842 inches.

This tap is used in machining shops, maintenance facilities, and field repair environments where damaged or insufficient threads need to be rethreaded to accept insert sleeves. Typical applications include engine component repair, aerospace and automotive thread restoration, and industrial equipment maintenance. The 1/4-20 UNC specification makes it a common fit for general-purpose fastener applications. It is installed by machinists, tool-and-die makers, and maintenance mechanics using a standard tap wrench or machine tapping setup.

Key Features

• 1/4-20 UNC thread profile engineered for STI (Screw Thread Insert) thread preparation
• Powdered metal construction provides wear resistance suitable for production use
• Oxide finish improves lubrication retention and reduces friction during cutting
• Plug chamfer (3-5 thread lead) allows use in through-holes and moderately deep blind holes
• H3 thread limit and 2B class of fit ensure proper tolerance for insert installation
• 3-flute design promotes efficient chip ejection ahead of the tap in through-hole applications

Compatibility

Designed as an OEM-style STI tap for use with 1/4-20 UNC helical wire thread inserts in through-hole tapping applications across ferrous and non-ferrous workpiece materials.

Installation Notes

This tap is installed by qualified machinists or maintenance mechanics using a tap wrench, tapping head, or CNC machine configured for the correct thread pitch. Always apply appropriate cutting fluid for the workpiece material and ensure the tap is aligned perpendicular to the workpiece surface before engaging. Inspect the tap for wear or chipping before each use, and never force a tap that has stalled — back it out to clear chips. Follow the insert manufacturer specifications for hole preparation depth and diameter prior to tapping.