Osg 8012102 Spiral Flute Sti Tap 1/4-28 Unf Hss

Product Description

The OSG 8012102 is a spiral flute STI (Screw Thread Insert) tap designed for cutting internal threads that accept Heli-Coil or similar wire thread inserts. Built from high-speed steel with an elektraLUBE surface finish, it runs a 50-degree helix angle that efficiently evacuates chips upward out of blind and through holes. The bottoming chamfer allows threading closer to the bottom of a blind hole than a taper or plug chamfer tap can reach. With an overall length of 2.5 inches and a 1-inch thread length, this tap is sized for typical hand-tap holders and standard tapping chucks used in machine shop and maintenance environments.

This tap is used wherever a 1/4-28 UNF STI thread form is required - repair applications on stripped aluminum, cast iron, or steel threads are the most common use case. The STI thread profile is oversized compared to a standard 1/4-28 tap, producing the correct minor and pitch diameters to receive a wire thread insert that restores the hole to a nominal 1/4-28 fastener. It is well suited for aerospace maintenance, automotive repair, and general machining where damaged fine-thread holes need reliable restoration without welding or oversizing the fastener.

Key Features

• STI thread form produces the oversized internal thread required for wire thread inserts such as Heli-Coils
• 50-degree spiral flute helix pulls chips up and out, reducing packing in blind holes
• Bottoming chamfer allows threading to within 1-2 threads of a blind hole bottom
• High-speed steel construction handles a wide range of workpiece materials including aluminum, mild steel, and cast iron
• elektraLUBE finish provides a dry-film lubricant layer that reduces friction and galling during tapping
• H3 thread limit provides consistent fit and tolerance control for insert installation

Compatibility

Designed for use in standard tapping chucks, T-handle tap wrenches, and CNC tapping cycles where a 1/4-28 UNF STI thread form is specified. Compatible with wire thread insert systems requiring an STI-dimensioned 1/4-28 UNF pilot hole.

Installation Notes

STI taps must only be used with the correct STI drill size for the insert being installed - using a standard 1/4-28 drill chart will produce an incorrect fit. Cutting fluid or tapping compound is recommended even with the elektraLUBE finish, particularly in ferrous materials. Back the tap out periodically to break and clear chips when working in deep blind holes. This tool is intended for use by machinists and maintenance technicians familiar with thread insert repair procedures.