Regal Cutting Tools 091388AS Extension Tap 5/16-18 Hss

Product Description

The REGAL CUTTING TOOLS 091388AS is a spiral point plug extension tap designed to cut right-hand internal threads in a wide range of materials. Built from high speed steel with a bright/uncoated finish, it runs a 5/16-18 UNC thread profile at an H3 thread limit, making it suitable for production and maintenance tapping where close thread tolerances are required. The plug chamfer allows the tap to start easily in through-holes while the spiral point pushes chips forward ahead of the cutting action. With an overall length of 4 inches and a thread length of 1.125 inches, this tap reaches into recessed or deep-clearance holes where standard-length taps cannot reach. It is sold individually and is typically used by machinists, maintenance technicians, and tool-and-die professionals.

This tap is suited for tapping through-holes in ferrous and non-ferrous materials including low, medium, and high carbon steel, free machining steel, alloy steel, stainless, precipitation hardened stainless, nickel alloy, cast iron, wrought aluminum, and various cast and die casting aluminum grades. The extended reach is particularly useful in fixture work, blind assemblies with deep bosses, or any application where a standard tap shank would contact the workpiece before full thread engagement is achieved. The reduced shank design and 0.238-inch square drive size are compatible with standard tap wrenches and machine holders sized for this range.

Key Features

• Spiral point geometry pushes chips forward, keeping flutes clear during through-hole tapping
• Plug chamfer provides easy thread start with 3 to 5 chamfered threads
• H3 thread limit holds close tolerances for 3B class of fit applications
• 4-inch overall length gives extended reach for recessed or deep-clearance hole tapping
• Reduced shank diameter of 0.240 inches allows entry into tighter bore approaches
• High speed steel construction handles a broad range of workpiece materials including stainless and nickel alloys

Compatibility

Designed for use in standard tap wrenches, T-handle tap wrenches, and machine tapping setups accepting a 0.238-inch square drive for the 5/16-18 UNC thread size range. Compatible material applications include alloy steel, aluminum, cast aluminum, cast iron, die casting aluminum, free machining steel, high carbon steel, low carbon steel, medium carbon steel, nickel alloy, precipitation hardened stainless, stainless, and wrought aluminum.

Installation Notes

Tapping operations should be performed by a qualified machinist or maintenance technician following standard shop safety practices. Always ensure the workpiece is securely fixtured and the tap is properly aligned with the drilled hole before applying torque to avoid tap breakage. Use an appropriate cutting fluid for the workpiece material to extend tool life and improve thread finish. When using in a machine tapping setup, confirm the tap holder provides adequate float to prevent side loading on the reduced shank.