Heli-coil 5CPA Hand Sti Tap 5/16-18 Unc H4 Plug Chamfer

Product Description

The HELI-COIL 5CPA is a hand STI tap designed to cut threads for Screw Thread Insert installation in 5/16-18 UNC threaded holes. Built from high speed steel with a bright finish, it features an H4 thread limit and a plug chamfer for general through-hole and blind-hole starting. With four flutes and a Class 2B fit, it produces accurate oversize threads that accept helical wire inserts, restoring or reinforcing thread strength in metal components. Overall length is 2.9375 inches with a thread length of 1.25 inches. Licensed tradespeople and experienced machinists use this tap when repairing stripped threads in aluminum, steel, and similar base materials.

This tap is suited for field repair and shop applications where helical wire thread inserts are required. It is commonly used in HVAC equipment repair, machinery maintenance, and industrial assembly where original threads have been stripped or damaged. The plug chamfer style makes it appropriate for both through-holes and deeper blind-hole applications with adequate clearance. The 5/16-18 UNC thread form is one of the most common coarse-thread sizes encountered across mechanical and HVAC equipment.

Key Features

• 5/16-18 UNC thread form with H4 thread limit for STI oversize thread cutting
• Plug chamfer design suitable for through-holes and blind holes with clearance
• 4-flute geometry for balanced chip evacuation and stable thread formation
• High speed steel construction for durability across a range of base materials
• Bright finish with no coating buildup, maintaining precise dimensional tolerances
• Class 2B fit for proper insert seating after tap operation

Compatibility

Designed for use with HELI-COIL STI thread insert installation systems in 5/16-18 UNC applications. Produces threads sized to accept standard helical wire inserts of the corresponding thread size.

Installation Notes

This tap is installed by hand using a standard tap wrench. Ensure the workpiece is securely fixtured before tapping. Apply appropriate cutting fluid for the base material to extend tool life and improve thread quality. Follow the insert manufacturer's drill size recommendations before tapping to achieve correct minor diameter for STI threads.