Incorrect, these work with stranded wire. If you check this sheet, you will see the compatible stranding patterns:
http://www.idealindustries.com/media...h-in_32-34.pdf
If your wire is finely stranded (like a lamp cord) you should NOT tin the ends and use these connectors anyway, as I'm pretty sure none of the push type connectors are approved for tinned ends. If you need to connect to finely stranded wire, the spring lever connectors are a better bet.