Osg 1663900 Straight Flute Tap 7/8-14 Unf Plug 3B Hss

Product Description

The OSG 1663900 is a straight flute tap designed to cut internal left-hand threads in a 7/8-14 UNF thread form. Built from high-speed steel with a bright/uncoated finish, this tap is suited for plug chamfer starting, making it appropriate for through-hole and most general-purpose tapping applications. It carries a 3B class of fit and an H4 thread limit, giving machinists and metalworkers the tolerance control needed for standard fastener assemblies. The overall length is 4-11/16 inches with a thread length of 2-7/32 inches and a shank diameter of 0.697 inches. This tool is intended for use by professional machinists, toolroom technicians, and trade fabricators working with precision threaded assemblies.

The OSG 1663900 is rated for use in a range of workpiece materials including aluminum, cast aluminum, cast iron, high-carbon steel, low-carbon steel, and medium-carbon steel. The left-hand thread direction makes it specifically applicable where reverse-thread fasteners are required, such as in certain mechanical assemblies, rotating shaft components, or equipment subject to counter-clockwise torque loads. Its 4-flute, straight-flute geometry provides stable cutting action in these materials when used in appropriate drilling and tapping setups.

Key Features

• Left-hand 7/8-14 UNF thread form for reverse-thread applications
• Plug chamfer for general-purpose through-hole and blind-hole entry
• H4 thread limit with 3B class of fit for standard tolerance fastener assemblies
• High-speed steel construction for durability across ferrous and non-ferrous materials
• 4 straight flutes provide stable chip control and cutting geometry
• Bright/uncoated finish suitable for use with cutting fluids across multiple material types

Compatibility

Rated for use in aluminum, cast aluminum, cast iron, high-carbon steel, low-carbon steel, and medium-carbon steel. Part of the OSG Series 101L tap line.

Installation Notes

This tap should be installed and operated by a qualified machinist or toolroom professional familiar with tapping procedures. Always secure the workpiece and ensure the tap is properly aligned with the pilot hole before engagement. Use an appropriate cutting fluid for the workpiece material to reduce heat and extend tool life. Inspect the tap for wear or chipping before each use and replace if thread quality degrades.