Sumitomo 16GC258 Pcbn Turning Insert 3/8 in Ic Diamond

Product Description

The SUMITOMO 16GC258 is a polycrystalline cubic boron nitride (PCBN) turning insert designed for machining hard materials on CNC lathes and turning centers. Manufactured to ANSI code NUVNMA331 and ISO code NU-VNMA160404, this insert features a 35-degree diamond shape, a 3/8 inch (0.3750 inch) inscribed circle, and a negative rake geometry with a clearance code of N and tolerance code of M. The BN350 grade is uncoated PCBN, suited for interrupted or continuous cuts on hardened steels, cast irons, and similar hard workpiece materials. Machinists and tool crib professionals handling precision turning applications will recognize the VNMA-style geometry immediately.

This insert is applied in hard turning operations where conventional carbide tooling reaches its limits. It is suited for finishing passes on hardened steels and hard ferrous materials in both production and job-shop environments. The 35-degree diamond shape and 1/64 inch (0.0156 inch) corner radius make it appropriate for contour turning and light finishing cuts. The insert is held by clamp and pin methods, consistent with standard VNMA-style toolholders used across CNC turning applications in automotive, aerospace, and general precision machining.

Key Features

• PCBN insert material (BN350 grade) for hard material turning
• 35-degree diamond insert shape with negative rake geometry
• 3/8 inch inscribed circle, 3/16 inch insert thickness
• 1/64 inch corner radius for finish turning and light contouring
• Uncoated for direct PCBN performance without coating interference
• Compatible with clamp and pin holding methods (VNMA-style toolholders)
• Meets ANSI and ISO 13399 standards

Compatibility

Designed as an OEM-style replacement insert conforming to ANSI code NUVNMA331 and ISO code NU-VNMA160404, fitting standard VNMA-style insert toolholders that accept a 35-degree diamond insert with clamp and pin retention.

Installation Notes

Installation is performed by qualified machinists or toolroom personnel. Power down and lock out the machine spindle before seating or indexing the insert. Use the appropriate torx or hex key to secure the clamping screw to the toolholder manufacturer's specified procedure. Inspect the insert pocket and seating surfaces for chips or debris before mounting to ensure proper insert contact and runout.