Well, I went to that site and put in all the required details. But first I queried whether they supplied mats with fittings attached, rather than just holes and they replied yes. Then they ask me this question. I've emailed them back to say, have they made a mistake but I'm wondering if I need to be confident that I'm ordering the correct size of fittings.
If people can say, no, they're all the same, then no worries.