UNF, UNC, Metric, Metric fine, BA, BSF....
Wouldn't life be much easier if there was ONE standard for bolts and threads.
Anyway.  H reg Discovery 200tdi.  Rear caliper bolts, the ones that bolt the caliper to the axle case.  What thread?  I reckon either 7/16" UNF or 10*1.25 mm.  What length?
I've already got one snapped bolt and the others are a little too tight for comfort so they need replacing soon as.  Trouble is, I need to know what bolts to buy and what size tap to clean the threads.