Osg 3147303 Straight Flute Tap 1/4-20 Unc Bottoming

Product Description

The OSG 3147303 is a straight flute bottoming tap designed for cutting internal threads in blind and through holes requiring full thread depth close to the bottom. Manufactured from cobalt high-speed steel with a nitride coating, it is built for durability and wear resistance in production tapping applications. The tap cuts a 1/4-20 UNC right-hand thread with a bottoming chamfer, meaning it has minimal lead-in and can thread nearly to the base of a blind hole. With 4 flutes and an H7 thread limit, it holds tight tolerances suitable for precision assemblies. Machinists and tool-and-die professionals install this tap in drill presses, CNC machining centers, and tapping arms.

The OSG 3147303 is suited for tapping plastic materials and similar low-resistance workpieces. Its bottoming chamfer makes it the correct choice when the full thread must extend as deep as possible into a blind hole, often used as the finishing tap in a two-tap or three-tap sequence following a spiral point or plug tap. The cobalt construction handles moderate heat buildup during dry or minimal-lubrication tapping cycles. This tap fits standard 1/4-inch tap holders and collets used in manual and CNC setups.

Key Features

• Bottoming chamfer for threading close to the bottom of blind holes
• Cobalt high-speed steel construction for extended wear life
• Nitride coating reduces friction and improves tool longevity
• H7 thread limit for controlled tolerance in precision fits
• 4 straight flutes suited for short-chip materials such as plastic
• Right-hand thread, no coolant-through requirement

Compatibility

Designed as an OEM-style replacement tap for standard 1/4-20 UNC threading operations in compatible tap holders and collets accepting a 0.255-inch shank diameter.

Installation Notes

Install this tap in a properly sized tap holder or collet matched to the 0.255-inch shank diameter. Ensure the workpiece is securely fixtured and the pilot hole is drilled to the correct tap drill size for 1/4-20 UNC before tapping. Apply appropriate cutting fluid or follow the machine tool manufacturer's lubrication guidance for the workpiece material. Inspect tap condition regularly and replace when cutting torque increases noticeably or thread quality degrades.