Flawed test? What gears have I?

A sure-grip is the type of carrier within the 3rd member. You either have an open carrier (like yours) or you have a sure-grip. Like Rocky said you can buy just a sure-grip but you'll have to use your gears or you can buy a complete 3rd member with lower gears and a sure-grip. If you've never set up gears you'd be best off buying a complete 3rd member IMO. Their not cheap but if you've never set one up having it done by a professional isn't cheap either.