Hi guy's. The JJ stamped into the wheel denotes that it is a 'double sided safety rim', that means it has the little ridge around the wheel that you need a bead breaker for. Early, early cars (FX-HR, I think) didn't have safety rims at all, then they introduced 'J' wheels (single sided safety rims) and later 'JJ' wheels. So all wheels manufactured or sold in Australia after a certain date had to have 'JJ wheels. If my memory serves me right, early HQ GTS wheels were imported from USA/Canada (Chev/Pontiac) until ROH started manufacturing them in Oz. I believe the rim part of the wheel (6")to be the same regardless of whether it had a GTS or standard center, the only rim that was different was on a one tonner wheel. Hope I haven't confused you. Rob.