Bryan.
That could have been me, as I posted a while back, of the good honest service given by, Roger Buse when he was the UK distributor for Hegner products.
At the time I contacted him for the supply of standard blade clamps and I was going to order the both sizes, but on his honest advice that the larger size clamp would grip all blades without a problem, I just ordered that size, and have been using them ever since with all size blades from, twelve down to size one, with no problem, having said that the blades I use most are number three, five and seven.
Hope this is of help.
Best Regards.
Chris R.