Just looking at the Grivel G12 with...
Just looking at the Grivel G12 with the Cramp-O-Matic front bail. Question: What size range boots is the XL version designed for?
These crampons only come in one size with the standard center bar. You can purchase the Grivel long bar separately which adds 30mm more ( long bar is 190mm) space to accommodate larger boots. Grivel advertises that the standard center bar should fit up to a size EU 47, which is US 14, though this would be unlikely in a pair of double mountaineering boots. From personal experience, I've fitted climbers with US 15 Scarpa Inverno plastic boot with the long bar and it fits well.
Check out the Grivel Long Flex Bar: http://www.backcountry.com/grivel-flex-long-bar