Chippy,
On my last trip away last month we decided to take 2 12x18 tarps so I had my ultrarig, and one of the boys went and bought another 12x18. Me thinking that all 12x18 would be the same in relation to eyelets.
Well they are not the ultrarig takes 20 poles and the durarig my mate has takes only 16, so our idea of joining them together did not work out.
when buying look at how many eyelets they have for the size of the tarp, the better ones have more eyelets, and in 40knots you will want everyone of them
Jet