In reply to reachingoceans:
Choosea brand and stick to that size, I've got a mixture of imperial and metric T-nuts/bolts on my wall and it's a bit of a pain, this is because I bought a metolius set of holds with nuts, and then some different ones from another manufactuer, and youend up with a bit too much of amish mash, its workaroundable, but abit of a pain.