Rex-Lee Diamond Mounted Points – Ø 3.0mm Our Precision Diamond mandrels are made from a single piece of steel and are hardened for maximum rigidity to best meet your application need. Diamond bonding, the diamond mandrels are utilized primarily for jig grinding of carbide tooling. It also used for jig and precision grinding of small holes in carbides, glass, ceramics, sapphire and many of tough, super alloys that are being machined.