Heli-coil 5905-5 Spiral Flute Sti Tap 5/16-18 Unc

Product Description

The HELI-COIL 5905-5 is a spiral flute STI (Screw Thread Insert) tap designed to cut threads for helical wire thread inserts in a single pass. Made from high-speed steel with a bright finish, this tap produces a 5/16-18 UNC thread with a 3B class of fit, suited to precision insert installation. The bottoming chamfer allows threading close to the bottom of a blind hole, making it the right choice when full thread depth is required right to the base of the bore. With 3 right-hand spiral flutes and an H3 thread limit, it delivers accurate, consistent thread form for insert prep work across a range of base materials.

This tap is used in maintenance, repair, and manufacturing applications where damaged or stripped threads are being reclaimed using helical wire inserts. It is the correct first step before installing a 5/16-18 UNC HELI-COIL or compatible wire thread insert. Typical install scenarios include engine component repair, equipment maintenance in industrial settings, and field repair of tapped holes in aluminum, cast iron, or steel. It is operated by hand tap wrench or low-speed machine tapping on a drill press or tapping machine.

Key Features

• 5/16-18 UNC thread form with H3 thread limit for accurate STI oversized thread profile
• Bottoming chamfer allows threading to the base of blind holes
• 3 right-hand spiral flutes for chip evacuation during tapping
• High-speed steel construction for durability across common base materials
• 3B class of fit ensures proper engagement geometry for wire thread inserts
• Overall length of 2-15/16 inches with a 0.381-inch shank diameter for standard tap wrench or holder compatibility

Compatibility

Designed for use in STI tapping operations prior to installation of 5/16-18 UNC helical wire thread inserts. Intended for use with compatible HELI-COIL or equivalent insert installation systems requiring a 3B class of fit thread.

Installation Notes

This tap is installed by a machinist, maintenance technician, or qualified tradesperson using a tap wrench or low-speed tapping setup. Always ensure the workpiece is secured and the bore is drilled to the correct STI drill size before tapping. Use appropriate cutting fluid for the base material to extend tap life and improve thread quality. Do not use excessive force or high spindle speeds, as HSS taps are susceptible to breakage under torsional overload.