Osg 2957400 Spiral Flute Tap 3/8-16 Unc 2 Flute Modified Bottoming

Product Description

The OSG 2957400 is a spiral flute tap designed to cut 3/8-16 UNC internal threads in production and maintenance machining applications. Built from vanadium high-speed steel with a bright, uncoated finish, this tap runs a 50-degree helix angle that efficiently evacuates chips up and out of the hole during the threading operation. The modified bottoming chamfer allows the tap to thread close to the bottom of a blind hole while still providing enough lead to start cleanly. At 2.938 inches overall length with an H3 thread limit, it holds a 3B class of fit across a consistent tolerance window.

This tap is suited for threading aluminum and similarly machinable non-ferrous materials in blind-hole applications where chip evacuation is critical. The spiral flute geometry makes it a practical choice for CNC tapping cycles and hand tapping operations where broken taps from chip packing are a concern. It is a single-piece, right-hand thread, right-hand flute tool sold individually. Machinists, toolroom technicians, and maintenance mechanics are the primary users of this type of tap in both shop and field contexts.

Key Features

• 3/8-16 UNC thread form, right-hand thread and right-hand flute direction
• Modified bottoming chamfer for threading near the bottom of blind holes
• 50-degree helix angle promotes upward chip evacuation in blind-hole tapping
• Vanadium high-speed steel construction for wear resistance in aluminum and soft metals
• H3 thread limit, 3B class of fit for standard tolerance internal threads
• Bright, uncoated finish — no coating buildup concerns on regrind

Compatibility

Designed for use in standard 3/8-16 UNC blind-hole tapping applications, particularly in aluminum workpieces. Compatible with tap handles, tapping heads, and CNC spindles accepting the Series 295 shank profile with a 0.381-inch shank diameter and 0.286-inch square drive.

Installation Notes

This tap is installed by licensed machinists or qualified toolroom personnel following standard threading practices. Secure the workpiece and verify correct tap drill size for 3/8-16 UNC before starting. Use appropriate tapping fluid or cutting oil for the workpiece material to extend tool life and improve thread finish. Inspect the tap for chipping or wear before each use and never force a tap that has stopped advancing, as spiral flute taps in blind holes can break under side load if chips pack the flutes.