Osg 1660200 Straight Flute Tap 1/4-20 Unc Bottoming Hss

Product Description

The OSG 1660200 is a straight flute bottoming tap designed for cutting internal left-hand threads to a 1/4-20 UNC specification in a range of ferrous and non-ferrous materials. Built from high-speed steel with an oxide coating, this tap operates in the 3B class of fit with an H3 thread limit, delivering tight dimensional control suited to production and maintenance threading applications. The bottoming chamfer allows threading to the bottom of blind holes where standard or plug chamfer taps cannot reach. Overall length is 2.5 inches with a thread length of 0.854 inches. It is installed by machinists and maintenance technicians using a tap wrench or machine holder.

This tap is appropriate for use in aluminum, cast aluminum, cast iron, low-carbon steel, medium-carbon steel, and high-carbon steel. The left-hand thread direction makes it suitable for applications where standard right-hand threads would loosen under torque, such as certain rotating assemblies or where reverse-thread fasteners are required by design. It fits the OSG 101L series and is suited to both manual and machine tapping operations in job shop, production, and field maintenance settings.

Key Features

• Bottoming chamfer for threading to the bottom of blind holes
• Left-hand thread direction for reverse-thread applications
• High-speed steel construction with oxide coating for wear and chip resistance
• 3B class of fit with H3 thread limit for consistent, inspectable thread geometry
• 4 straight flutes suited to through-hole and short blind-hole threading
• Compatible with multiple ferrous and non-ferrous base materials

Compatibility

Designed as an OEM-style replacement or direct substitute tap for 1/4-20 UNC left-hand bottoming applications across standard machine and hand tapping setups. Material suitability includes aluminum, cast aluminum, cast iron, low-carbon steel, medium-carbon steel, and high-carbon steel per manufacturer specification.

Installation Notes

A licensed machinist or qualified maintenance technician should install this tap using a properly sized tap wrench or machine holder that matches the square drive dimensions. Before tapping, verify the drilled hole diameter matches the recommended tap drill size for 1/4-20 UNC threads and that hole depth allows for the bottoming chamfer engagement. Use appropriate cutting fluid for the material being tapped to reduce heat and extend tap life. Left-hand taps require counterclockwise rotation to advance - confirm thread direction before beginning the operation to avoid tap breakage.