Osg 1730801 Spiral Point Tap 5/16-18 Unc 3 Flute

Product Description

The OSG 1730801 is a spiral point plug tap designed for threading 5/16-18 UNC holes in ferrous and stainless steel materials. Built from vanadium high-speed steel (HSS-E) with a steam oxide coating, this tap handles hardened steel, low-carbon steel, medium-carbon steel, and stainless steel applications. The spiral point geometry pushes chips forward ahead of the cut rather than packing them in the flutes, making it well suited for through-hole tapping. With an H3 thread limit and 3B class of fit, it produces threads within standard tolerance for most commercial fastener applications. Overall length is 2.72 inches and thread length is 0.669 inches.

This tap is used in machine shop, maintenance, and production environments where through-hole threads in steel are required. The plug chamfer - typically 3 to 5 leading threads - makes it the standard choice for starting in a pre-drilled through hole without needing a taper tap first. It is appropriate for use in drill presses, CNC machining centers, tapping heads, and hand tapping with a T-handle. Typical applications include structural fabrication, equipment repair, and production threading in ferrous metals.

Key Features

• 5/16-18 UNC thread form, H3 thread limit, 3B class of fit for standard commercial tolerance
• Vanadium high-speed steel (HSS-E) construction for improved wear resistance over standard HSS
• Steam oxide coating reduces friction and provides light corrosion resistance during storage and use
• Spiral point design pushes chips forward - optimized for through-hole tapping
• 3 flutes, plug chamfer, right-hand thread direction
• No coolant-through feature; suitable for flood coolant or tapping fluid applied externally

Compatibility

Designed for threading 5/16-18 UNC through holes in hardened steel, low-carbon steel, medium-carbon steel, and stainless steel. Compatible with standard 5/16-18 tapping chucks, tapping heads, and T-handle tap wrenches.

Installation Notes

A licensed machinist or qualified maintenance technician should verify correct tap drill size before use - a 17/64-inch drill is standard for 5/16-18 UNC at approximately 75 percent thread engagement. Secure the workpiece fully before tapping to prevent movement. Apply appropriate tapping fluid or cutting oil for the material being threaded; do not run dry in steel. Reverse the tap periodically when hand tapping to break chips and reduce the risk of tap breakage.