Hertel K008078AS 4-40 Unc Bottoming Tap 3 Flute Hss

Product Description

The HERTEL K008078AS is a straight flute bottoming tap designed for cutting internal threads in through-holes and blind holes where threads must extend close to the bottom. Manufactured from high-speed steel (HSS) with a bright/uncoated finish, this tap cuts a 4-40 UNC right-hand thread and is suited for use in small-fastener tapping operations common in precision machining, electrical panel fabrication, and light mechanical assembly. The bottoming chamfer — typically 1 to 2 thread leads — allows threading to near the full depth of a blind hole. With a 3-flute straight-flute geometry, it provides good chip clearance in short-chipping materials and maintains rigidity through the cut.

This tap is intended for use in ferrous and non-ferrous metals, plastics, and similar materials where a 4-40 UNC thread form is specified. It is suited for manual tapping with a tap wrench or low-speed machine tapping on drill presses, CNC machining centers, and tapping heads. The compact overall length of 1.875 inches makes it practical for use in tight workpiece geometries or toolholders with limited clearance. Machinists, tool-and-die makers, and maintenance mechanics installing small machine screws in electrical or mechanical assemblies will find this tap appropriate for production and repair work alike.

Key Features

• Bottoming chamfer for threading to near full depth in blind holes
• High-speed steel construction provides good wear resistance for general-purpose tapping
• Bright/uncoated finish suitable for use with cutting oil or tapping fluid
• 3 straight flutes for chip clearance in short-chipping materials
• H1 thread limit for close-tolerance thread fits
• Right-hand thread direction, standard UNC form

Compatibility

Designed as a standard replacement or general-purpose tap for any application requiring a 4-40 UNC internal thread. Compatible with standard tap wrenches, T-handle wrenches, and machine tapping holders accepting a 0.141 inch shank diameter.

Installation Notes

Secure the workpiece firmly before tapping and ensure the correct tap drill size has been used for 4-40 UNC thread engagement. Apply a suitable cutting fluid or tapping compound throughout the operation to reduce heat and extend tap life. For machine tapping, use a tapping head or floating holder to minimize axial load. Inspect the tap for chipping or wear before each use — a dull or damaged tap in a blind hole can result in breakage that is difficult to remove.