Heli-coil 5CSB Spiral Point Sti Tap 5/16-18 Unc

Product Description

The HELI-COIL 5CSB is a spiral point STI tap designed to cut threads for Screw Thread Insert installation in 5/16-18 UNC applications. Ground from high-speed steel with a bright, uncoated finish, this plug chamfer tap drives chips forward ahead of the cutting edge, making it well suited for through-hole tapping operations. It measures 2-15/16 inches overall length with a 1-1/4 inch thread length, and conforms to an H3 thread limit and 3B class of fit for precise insert-ready thread geometry. Licensed machinists, maintenance mechanics, and trade technicians reach for this tap when restoring or creating threads that will accept wire-type helical inserts.

This tap is used wherever stripped or damaged threads need to be reclaimed using a wire insert system, including threaded fastener bosses in aluminum, cast iron, and steel housings common to HVAC equipment, pumps, compressors, and general industrial assemblies. The STI (Screw Thread Insert) thread form produces an oversized thread profile that, once a helical insert is installed, results in a finished thread matching the original 5/16-18 UNC specification. It is appropriate for both production and field repair work.

Key Features

• Spiral point geometry pushes chips forward, reducing clogging in through-hole applications
• STI UNC thread form produces the oversized pilot thread required for helical wire insert installation
• High-speed steel construction provides durability across a range of base materials
• H3 thread limit and 3B class of fit deliver consistent, insert-ready thread accuracy
• Plug chamfer (3-5 thread lead) balances cutting performance and ease of starting
• Bright, uncoated finish allows visual inspection of cutting edges before and after use

Compatibility

Designed for use in standard 5/16-18 UNC STI thread insert applications where a helical wire insert will be installed to restore or create a 5/16-18 UNC finished thread.

Installation Notes

This tap should be installed by a qualified machinist or maintenance mechanic using a properly sized tap handle or machine spindle. Power down and de-energize or depressurize any assembly before performing thread repair work. Use cutting fluid appropriate for the base material to extend tap life and improve thread quality. Do not force the tap if resistance increases unexpectedly - back off to clear chips before continuing.