Brake Rotor Separation

The wheel hub is the thing the rotor slides onto with the 6 studs in it.

 

The part that broke off was the part with hole for the studs. Thanks.

 

I've only seen it a couple times in my career. First time on a Toyota. The others I remember as being Chevy's.
What I haven't seen in a long time is someone who wears their brakes down metal on metal and continues driving until the rotor surface is worn to the cooling fins. Ouch.

 

The Hub.

 

Stick a washer, or a coin, or whatever hard thing really, on each side where the pad hits. Measure the rotor & both whatevers.

Take both whatevers, measure them, subtract that from above = actual rotor thickness. All you're doing is using your whatevers to get over the wear lip on the rotor with a standard pair of straight-jaw calipers.