What kind of project and where did you get the one shown?

Millimeters are kind of small, do you mean centimeters?

Why do you thing they are an electrical supply item? They just look like some kind of spacer for something. I'd doubt that they are a generic item. Probably part of something else.

Your picture, unfortunately, does not provide much info. Can you photograph these pieces from a couple of different angles? I can't make any sense of what I'm supposed to be looking at....