Osg 8018400 Spiral Flute Sti Tap 1/2-20 Unf Hss

Product Description

The OSG 8018400 is a spiral flute STI (Screw Thread Insert) tap designed to cut 1/2-20 UNF internal threads intended to accept Heli-Coil or equivalent threaded inserts. Built from high-speed steel with a bright finish, this tap features a 50-degree helix angle that promotes efficient chip evacuation in blind and through-hole applications. The bottoming chamfer allows the tap to thread nearly to the bottom of a blind hole, maximizing usable thread depth. With 4 flutes and an H3 thread limit, it delivers consistent dimensional control in a range of ferrous and non-ferrous materials. Machinists and tool and die professionals install this tap in manual and CNC threading operations.

This tap is suited for threading operations on aluminum, carbon steel, cast iron, and hardened steel workpieces. It is used wherever an STI oversize thread is required to prepare a hole for a threaded insert, a common repair and manufacturing technique in aerospace, automotive, and general machining shops. The 3-3/8-inch overall length fits standard tap holders and extension arms, and the right-hand flute direction matches conventional right-hand threading setups.

Key Features

• 1/2-20 UNF thread form sized for STI insert preparation
• 50-degree helix angle promotes upward chip flow for cleaner blind-hole threading
• Bottoming chamfer threads close to the base of a blind hole
• H3 thread limit provides controlled tolerance for consistent fit with threaded inserts
• High-speed steel construction handles aluminum, carbon steel, cast iron, and hardened steel
• 4-flute design adds rigidity and surface finish quality at the thread form

Compatibility

Designed for use in STI thread insert applications requiring a 1/2-20 UNF oversize tap; compatible with standard tap holders accepting a 0.367-inch shank diameter. Suitable for material applications including aluminum, carbon steel, cast iron, and hardened steel per OSG Series S108 specifications.

Installation Notes

This tap is installed by a machinist or toolroom technician using a tap wrench, tapping head, or CNC rigid tapping cycle. Secure the workpiece before tapping and apply appropriate cutting fluid for the workpiece material to reduce heat and extend tap life. Never reverse a spiral flute tap under power without confirming the machine supports synchronized retract. Inspect the tap for wear or chipping before each use, as a damaged tap can seize in hardened materials.