Osg 1812500 Hand Sti Tap 5/16-18 Unc H3 Bottoming

Product Description

The OSG 1812500 is a hand STI tap designed to cut Screw Thread Insert (STI) threads in a range of metallic base materials. It produces an oversized internal thread that accepts standard helical thread inserts, restoring or upgrading threaded holes to their original nominal size. The tap is ground to an H3 thread limit, which controls pitch-diameter tolerance for consistent insert fitment. Four flutes and a bottoming chamfer allow the tap to thread close to the bottom of a blind hole. Overall length is 2-23/32 inches with a 1-1/8-inch thread length and a 0.318-inch shank diameter. Material is High Speed Steel with a bright finish.

This tap is suited for production and maintenance applications where threaded holes in aluminum, carbon steel, cast iron, or hardened steel have been stripped or need to be converted to insert-style threads. The bottoming chamfer is especially useful in shallow blind holes where a plug or taper chamfer would leave unthreaded material at the base of the bore. Typical users include machinists, millwrights, and maintenance technicians working on engine components, structural assemblies, and industrial equipment.

Key Features

• STI thread form for 5/16-18 UNC thread inserts, H3 pitch-diameter limit
• Bottoming chamfer for threading to the base of blind holes
• Four flutes for chip clearance and cutting efficiency
• High Speed Steel construction for durability across multiple materials
• Bright finish, suitable for use with cutting fluid
• Compact 2-23/32-inch overall length for confined-space access

Compatibility

Designed for use in aluminum, carbon steel, cast iron, and hardened steel workpieces requiring 5/16-18 UNC STI threads. Intended for use with standard helical thread inserts in 5/16-18 UNC nominal size.

Installation Notes

Installation is typically performed by a machinist or maintenance technician using a tap wrench or tapping fixture. The workpiece must be securely clamped and the pilot hole drilled to the correct STI tap drill size before tapping. Apply an appropriate cutting fluid for the base material to extend tap life and improve thread finish. Do not force the tap; back off periodically to break chips, particularly in blind holes.