Osg 1298200 Spiral Flute Extension Tap 1/4-28 Unf H3 Hss

Product Description

The OSG 1298200 is a spiral flute extension tap designed for right-hand threading of 1/4-28 UNF threads in production and maintenance applications. Built from high-speed steel with a bright, uncoated finish, this plug-chamfer tap features a 50-degree helix angle that promotes chip evacuation in through-hole and blind-hole operations. The 6-inch overall length provides the reach required when threading recessed or hard-to-access holes. With an H3 thread limit and a 3B class of fit, it delivers consistent tolerance control on precision threaded assemblies. Three flutes and a right-hand flute direction make it compatible with standard tapping setups. Weighing 0.095 pounds, it is suited for hand tapping or machine tapping in toolrooms, job shops, and maintenance environments.

This tap is intended for threading aluminum, carbon steel, and cast iron workpieces in applications where standard-length taps cannot reach. The reduced shank and extended neck length of 1.007 inches allow the tool to clear obstructions and engage deep within bossed or countersunk features. It is a strong fit for aerospace, automotive, and general manufacturing threading tasks where 1/4-28 UNF fastener threads must be cut to a 3B tolerance class. The plug chamfer makes it appropriate for through-holes or holes with adequate clearance at the bottom.

Key Features

• 1/4-28 UNF right-hand thread form with H3 thread limit for 3B class of fit
• 50-degree helix angle promotes efficient chip evacuation in spiral flute design
• 6-inch overall length provides extended reach for deep or recessed hole threading
• High-speed steel construction suited for aluminum, carbon steel, and cast iron
• Reduced shank with 0.255-inch shank diameter and 1.007-inch neck length for clearance in tight setups
• Bright uncoated finish; plug chamfer for general-purpose through-hole and open blind-hole use

Compatibility

Designed for threading 1/4-28 UNF holes in aluminum, carbon steel, and cast iron. Compatible with standard tap wrenches and machine tapping setups that accept a 0.255-inch shank with a 0.191-inch square drive. Part of the OSG Series 918 extension tap line.

Installation Notes

Power down or de-energize any machine tool before loading or removing this tap. Use appropriate cutting fluid matched to the workpiece material to extend tool life and improve thread finish. Verify that the tap holder or wrench is sized to the 0.191-inch square to prevent slippage. Follow applicable shop safety procedures and OSHA machine guarding requirements when operating tapping equipment.