Osg 0137101 Spiral Flute Tap 1/4-20 Unc Bottoming 3B Hss

Product Description

The OSG 0137101 is a spiral flute bottoming tap designed to cut 1/4-20 UNC internal threads in a wide range of ferrous materials. Built from vanadium high-speed steel with a steam oxide coating, it delivers reliable tap life in production and maintenance applications. The 45-degree right-hand helix angle evacuates chips upward out of the hole, making it well suited for blind-hole tapping where chip packing is a concern. With a 3B class of fit and H3 thread limit, the tap produces threads that meet standard tolerance requirements for general mechanical assembly. Overall length is 2.5 inches, and the shank diameter is 0.255 inches.

This tap is intended for use in stainless steel, high-carbon steel, low-carbon steel, and medium-carbon steel. The bottoming chamfer — typically 1 to 2 threads of lead — allows threading to the bottom of a blind hole, making it the correct choice when thread depth must be maximized. It is typically used as the finishing tap in a two- or three-tap sequence, following a taper or plug tap to start the thread. Machinists, tool-and-die makers, and maintenance technicians use this tap in both CNC tapping operations and manual tapping with a tap wrench or tapping fixture.

Key Features

• Bottoming chamfer for full-depth threading in blind holes
• 45-degree right-hand spiral flute for upward chip evacuation
• Vanadium high-speed steel construction for wear resistance in ferrous materials
• Steam oxide coating reduces friction and improves lubrication retention
• H3 thread limit, 3B class of fit for standard mechanical assembly tolerances
• Right-hand thread direction, 3 flutes

Compatibility

Designed for cutting 1/4-20 UNC threads in stainless steel, high-carbon steel, low-carbon steel, and medium-carbon steel workpieces. Fits standard 1/4-inch tap holders and tapping chucks sized for a 0.255-inch shank diameter.

Installation Notes

This tap is installed by a machinist or maintenance technician using a tap wrench, tapping handle, or CNC tapping chuck. Always use an appropriate cutting fluid or tapping compound for the workpiece material — especially when tapping stainless steel. Ensure the workpiece is securely fixtured and the tap is aligned perpendicular to the drilled hole before applying torque. As a bottoming tap, it should follow a taper or plug tap that has already started the thread to the required depth.