Thanks. I've contacted Apex and it is fourteen millimetres. I'm going to buy two sets. The postage is a shade over $80. I'll start another thread and sees if anyone who missed out on the group buy is still interested. A few extra sets probably wouldn't change the postage much.
Bugger I can't work out how to post a new thread. If anyone wants to contact me because they are interested in something, please pm me.