Osg 2916801 Spiral Flute Tap 4-48 Unf Modified Bottoming

Product Description

The OSG 2916801 is a spiral flute tap designed for cutting 4-48 UNF internal threads in a range of ferrous and alloy materials. Built from 3% vanadium high-speed steel with a steam oxide coating, this tap delivers consistent thread quality in applications where standard HSS tooling falls short. The modified bottoming chamfer allows threading close to the bottom of blind holes. With a 45-degree helix angle and right-hand flute direction, the spiral geometry efficiently evacuates chips upward, reducing the risk of chip packing in deeper holes. Licensed machinists and toolroom technicians are the primary users of this tap.

This tap is suited for precision threading in alloy steel, carbon steel, cast iron, stainless steel, die steel, and hardened steel workpieces. The 4-48 UNF thread form is common in small-diameter, fine-pitch applications such as instrument housings, electronic enclosures, optical mounts, and small mechanical assemblies. The 2B class of fit meets standard commercial tolerances for most threaded fastener applications requiring a free-running fit. Series 290 designation identifies this as part of OSG's standard spiral flute tap line.

Key Features

• 4-48 UNF thread form with H2 thread limit for controlled 2B class of fit
• 45-degree right-hand helix angle promotes upward chip evacuation in blind holes
• Modified bottoming chamfer for threading close to the base of blind bores
• 3% vanadium HSS construction for improved wear resistance over standard M2 HSS
• Steam oxide coating reduces friction and provides mild lubricity
• No coolant-through design - suitable for standard tapping with cutting fluid applied externally

Compatibility

Designed for cutting 4-48 UNF threads per ASME B1.1 standards in alloy steel, carbon steel, cast iron, stainless steel, die steel, and hardened steel. Compatible with standard tap holders and tapping heads accepting a 0.381-inch shank diameter.

Installation Notes

Secure the workpiece and ensure the tap is properly aligned to the drilled pilot hole before engagement to prevent tap breakage. Apply a suitable cutting fluid or tapping compound for the workpiece material, particularly when threading stainless or hardened steel. Use a tap wrench, tapping head, or CNC rigid-tapping cycle appropriate for the small diameter. Reverse the tap periodically when hand-tapping to break and clear chips, and never force a tap that shows signs of binding.