Heli-coil 04CSB Spiral Point Sti Tap 4-40 Unc Hss

Product Description

The HELI-COIL 04CSB is a spiral point STI tap designed for cutting threads in preparation for Heli-Coil thread insert installation. It is ground to STI (Screw Thread Insert) specifications, which produce an oversized thread profile that accommodates the installed insert and returns the finished hole to standard 4-40 UNC dimensions. Manufactured from high-speed steel (HSS) with a bright, uncoated finish, this tap features a plug chamfer and 2 flutes. Overall length is 2 inches, with a thread length of 11/16 inches. The H1 thread limit designation indicates a tight tolerance grind suited for close-tolerance insert work. Machinists and maintenance technicians use this tool in production and repair applications.

This tap is used wherever a 4-40 UNC Heli-Coil insert is being installed - including repair of stripped or damaged threads in aluminum, magnesium, cast iron, and steel components. Typical applications include aerospace maintenance, electronic enclosure repair, and general industrial thread restoration. The plug chamfer makes it suitable for through-hole tapping and for starting in a hole with adequate depth. It is sized for use with a standard tap wrench or machine holder appropriate for the shank diameter of 0.141 inches.

Key Features

• STI thread form ground oversize to accept Heli-Coil thread inserts, resulting in a finished 4-40 UNC thread after insert installation
• High-speed steel construction provides hardness and wear resistance for tapping ferrous and non-ferrous materials
• Bright, uncoated finish - no coating thickness to affect tolerance; suited for general-purpose use
• Plug chamfer (3-5 thread lead) allows easy starting in through holes and blind holes with sufficient depth
• H1 thread limit for tight dimensional control in insert-prep tapping
• 2-flute design promotes chip ejection in the spiral point configuration during through-hole tapping

Compatibility

Designed for use with Heli-Coil thread insert systems requiring a 4-40 UNC STI tapped hole. This tap prepares the hole for a standard 4-40 insert and is not interchangeable with standard 4-40 UNC taps.

Installation Notes

This tap should be installed and used by a qualified machinist or maintenance technician familiar with thread insert procedures. Ensure the workpiece is securely fixtured before tapping and use the appropriate cutting fluid for the base material being tapped. The spiral point design pushes chips forward, so use in through holes where chip clearance is available. Follow the Heli-Coil installation sequence - drill, tap with STI tap, chamfer if required, then install the insert - to achieve a properly sized finished thread.