[Last Dakotan]

The first one is a nickle plated diamond grinding wheel - unless you knew that.
Freep metalworking ping.

[mutley]

"The first one is a nickle plated diamond grinding wheel - unless you knew that. Freep metalworking ping."

With the diamond grit electroplated onto the metal.

The other one is a millstone.

[Ignatz]

The first one is a nickle plated diamond grinding wheel - unless you knew that.

Wow. Why would you want to grind nickel-plated diamonds? To make nickel-plated diamond dust?