Thanks James, but not the dimension I meant, where the central hole runs parallel, what length, but it does not matter as you have answered the question that they have been used on a Sierra which means they must have been machined (had material removed from their mounting face)otherwise they would not fit.
I have many center sections machined for a Sierra, I want in-machined centers but
If you get any more let me know we might be able to sort a deal.

Thanks

Steve