Osg 1120102 Straight Flute Tap 1/4-20 Unc Plug Hss

Product Description

The OSG 1120102 is a straight flute plug tap designed for cutting internal right-hand threads in ferrous and non-ferrous metals. Built from high-speed steel (HSS), it cuts a 1/4-20 UNC thread to a Class 3B fit with an H3 thread limit, making it suitable for close-tolerance tapped holes where thread accuracy matters. The plug chamfer - typically 3 to 5 threads of lead - provides a balance between starting ease and thread engagement, making it the most commonly specified chamfer style for through-hole and moderately deep blind-hole applications. Overall length is 2.5 inches with a thread length of 1 inch across 4 flutes.

This tap is used in machine shop, maintenance, and field repair work where 1/4-20 UNC threads must be cut or restored. The straight flute geometry is well suited for short-chipping materials including aluminum, cast aluminum, cast iron, low-carbon steel, medium-carbon steel, and high-carbon steel. It is appropriate for use in vertical or horizontal drilling machine setups, tapping heads, or hand tapping with a tap wrench. Machinists, millwrights, and field service technicians regularly spec this style of tap for general-purpose production and repair tapping operations.

Key Features

• 1/4-20 UNC thread form, Class 3B fit for standard close-tolerance applications
• H3 thread limit for consistent tolerance control in production tapping
• 4-flute straight flute design optimized for short-chipping materials
• Plug chamfer for reliable thread starting in through holes and shallow blind holes
• High-speed steel construction for durability across a broad range of workpiece materials
• No coolant-through requirement - compatible with flood coolant or tapping fluid applied externally

Compatibility

Compatible with aluminum, cast aluminum, cast iron, low-carbon steel, medium-carbon steel, and high-carbon steel workpieces. Part of OSG Series 101.

Installation Notes

This tap is installed by machinists and maintenance technicians using standard tapping equipment or a hand tap wrench. The workpiece should be securely fixtured and the pilot hole drilled to the correct tap drill size for 1/4-20 UNC before tapping begins. Apply a suitable tapping fluid or cutting oil appropriate to the workpiece material to extend tool life and improve thread quality. Follow standard shop safety practices including securing the workpiece and ensuring the tapping axis is aligned with the drilled hole to prevent tap breakage.