Osg 1660900 Straight Flute Tap 3/8-16 Unc Plug 3B Hss

Product Description

The OSG 1660900 is a straight flute plug tap designed for cutting left-hand internal threads to a 3/8-16 UNC standard. Manufactured from high-speed steel (HSS) with a bright/uncoated finish, it delivers reliable performance in general-purpose tapping applications. The plug chamfer provides a gradual thread lead-in, making it suitable for through-hole tapping. With 4 flutes and an H3 thread limit, this tap holds tight tolerances required by a 3B class of fit. Overall length is 2-15/16 inches with a thread length of 1-1/4 inches. Licensed machinists, tool-and-die makers, and maintenance mechanics are the primary installers of this tooling.

This tap is intended for use in through-hole tapping operations across a range of ferrous and non-ferrous materials. Rated material applications include aluminum, cast aluminum, cast iron, high-carbon steel, low-carbon steel, and medium-carbon steel. The left-hand thread direction makes it appropriate for spindles, fixtures, or assemblies where counter-rotation or reverse-thread requirements dictate left-hand fastener systems. It is part of the OSG Series 101L product line and is sold individually.

Key Features

• Left-hand thread direction for reverse-thread tapping applications
• Plug chamfer allows gradual thread engagement in through-hole work
• H3 thread limit and 3B class of fit for controlled tolerance threading
• 4 straight flutes provide chip clearance in short-chipping materials
• High-speed steel construction with bright/uncoated finish for general-purpose use
• No coolant-through requirement simplifies setup on standard machine tools

Compatibility

Designed for use in standard tapping chucks, tap handles, and CNC rigid-tapping setups that accept a 0.381-inch shank diameter. Compatible with the material types listed by OSG for Series 101L: aluminum, cast aluminum, cast iron, high-carbon steel, low-carbon steel, and medium-carbon steel.

Installation Notes

Install in a properly sized tapping chuck or floating tap holder to minimize side load on the flutes. Power down or de-energize the machine spindle before changing tooling. Ensure the workpiece is securely fixtured and the pilot hole diameter is correctly sized for 3/8-16 UNC before beginning the tapping operation. Left-hand taps require spindle rotation in the reverse direction relative to right-hand tapping - confirm machine settings before engaging the tool.