This boring head uses a standard triangular carbide insert 3/8 inscribed circle. Please check above for notes on condition. A ruler, tape measure, or coin may appear in the listing and is a size reference only. We primarily deal in industrial surplus. All items are described to the best of our abilities. We are more than happy to answer questions so please feel free to ask. We do not use stock photos and all pictures are of the actual item. The primary exceptions are for "new old stock" situations where multiple of the same item is available. We strive for complete satisfaction.