Heli-coil 4CPB Hand Sti Tap 1/4-20 Unc H2 Plug Chamfer

Product Description

The HELI-COIL 4CPB is a hand STI tap designed to cut threads for Screw Thread Insert installation in 1/4-20 UNC tapped holes. It carries an H2 thread limit and a plug chamfer, making it well suited for through-hole and moderately deep blind-hole applications. Machined from high-speed steel with a bright uncoated finish, the tap holds edge integrity through repeated use on steel, aluminum, cast iron, and similar materials. The 3-flute geometry provides adequate chip clearance for hand-tapping operations. Thread length is 1-1/8 inches and overall length is 2-23/32 inches.

This tap is used wherever a damaged or stripped 1/4-20 UNC thread needs to be reconditioned using a Heli-Coil or compatible wire thread insert system. Typical applications include engine component repair, equipment maintenance, aerospace assembly, and general metalworking where restored threads must meet Class 3B fit tolerances. It is installed by hand using a standard tap wrench and is sized to produce the oversized pilot hole thread that accepts the insert rather than a standard fastener thread.

Key Features

• STI thread form produces the correct oversized thread geometry for wire thread insert installation
• Plug chamfer allows entry in through-holes and moderately deep blind holes
• H2 thread limit provides consistent Class 3B fit tolerances
• High-speed steel construction resists wear across a range of workpiece materials
• 3-flute design provides chip clearance suitable for hand-tapping operations
• Bright uncoated finish - no coating to flake or interfere with thread dimensions

Compatibility

Designed as an STI tap for use with Heli-Coil and compatible wire thread insert systems requiring a 1/4-20 UNC oversized tapped hole to Class 3B fit.

Installation Notes

Installation is performed by hand using a tap wrench; power driving is not recommended for hand taps. Ensure the workpiece is securely fixtured and the pilot hole is drilled to the correct STI tap drill diameter before tapping. Apply cutting fluid appropriate to the workpiece material to reduce friction and extend tap life. Follow shop safety practices for rotating cutting tools and inspect the tap for wear or chipping before each use.