Spare wheel clamp lengths

Hi List,

Anyone have the respective tip to tip lengths of the spare wheel clamp?  I 
have one which is approx 6.5" tip to tip which I think is Spridget w/w.  I also 
have one which is approx 8" tip to tip which is MGB but I'm not sure if bolt 
on wheel MGB or w/w MGB - any correborating measurements out there?

Thanks

Daniel