It could be that Leitz provide their own custom collets, for their own custom shanks sizes, lets see what we can find...

A quick look on their website found this link: 5. Cutting tools with shank

If you confirm the Collet Chuck, they provide information on each and also a list of spare parts for the Chucks.

It looks as though they offer shank sizes from 6-24.5mm, what type of router have you got?

Cant confirm if it is a "cnc shank size" as cnc stands for? (Computer Numerical Controlled) :naughty:.

Lee