XT-Z 660 spark plug help

[shack]

Hi Guys, after a bit of (prob real basic) info please.
I'm swapping my plug for an Iridium (helped a lot on an F650 GSPD I had)to improve start up etc
I can only find my metric feeler guages (so what size gap do folk recommend- inc Yam!)
And what size spark plug spanner (I can only find my huge one, after a garage tidy) do I need.

Thanks in advance

PS any one got any good ideas (and cheap/free) for fixing a split in the seat, I was going to sew it, but the plastic it tough as and no leverage to get the two sides together.
Was considering gluing a leather patch (or even bit of inner tube!) I have a small sheepskin off cut I sit on for anything over about a 15mile trip so it doesn't need to look sexy, just functional
BTw it's a 1996 model
It's just a permanant wet patch at the moment