These are three of six very fine coasters that I tatted for my mother in law. I've used DMC Special Cordonnet No. 150 for them. (I don't think DMC carries it any longer). The diameter is 7 cm (just under 3 inch). They feature net stitch and concentric rings done in onion ring technique. I wouldn't call them onion rings though, because there's still space between the rings.