Osg 1603207 Straight Flute Tap 1/2-20 Unf Bottoming Hss

Product Description

The OSG 1603207 is a straight flute bottoming tap designed for cutting 1/2-20 UNF internal threads in through-holes and blind holes where thread engagement must extend close to the bottom. Built from high-speed steel with a nitride and oxide coating, this tap resists wear and surface galling under production conditions. It carries a 3B class of fit and an H3 thread limit, making it suitable for standard tolerance threaded assemblies. The 4-flute straight flute design provides good chip control and thread form stability in the materials for which it is rated. Machinists and tool-and-die technicians are the primary users of this tap in job shop and production environments.

This tap is rated for use in aluminum and cast iron. The bottoming chamfer - typically 1 to 2 threads of lead - allows threading to within a few threads of a blind hole bottom, making it the right choice for close-tolerance blind-hole work where a plug or taper tap cannot reach full depth. It is not suited for use as a first-pass tap in a virgin hole; bottoming taps are typically used as the final tap following a plug tap in a standard 3-tap sequence, or alone in pre-formed holes with adequate lead-in.

Key Features

• 1/2-20 UNF right-hand thread form, 3B class of fit, H3 thread limit
• Bottoming chamfer for threading close to the bottom of blind holes
• 4 straight flutes for solid chip formation in aluminum and cast iron
• High-speed steel construction with nitride and oxide dual coating for wear resistance
• Series 101C - no coolant-through requirement, suitable for manual and CNC tapping with flood or mist coolant

Compatibility

Designed for cutting 1/2-20 UNF internal threads in aluminum and cast iron workpieces. Intended for use in standard tap holders, floating tap holders, or manual tap wrenches accommodating a shank diameter of 0.367 inches and a square drive of 0.275 inches across the flat.

Installation Notes

Secure the workpiece fully before tapping and ensure the tap is started square to the hole axis. Power down or disengage the spindle before changing taps in a CNC or drill-press setup. Apply appropriate cutting fluid for the workpiece material - sulfurized oil or water-soluble coolant for cast iron, light cutting oil or kerosene-based fluid for aluminum. Bottoming taps should follow a plug tap to remove the majority of material; driving a bottoming tap into an untapped hole risks tap breakage and workpiece damage.