We own a Krogen 39 too. Our single flybridge hatch strut when it is collapsed measures 15-3/16" long, and has cylinder diameter of 11/16". The cylinder only measures 11-1/4". When extended, 9-1/2" of the shaft is outside of the cylinder. There is no label, or other information that I can see on it.
I would definitely recommend calling the Krogen office. We speak regularly with the head office in Florida at (800) 247-1230, and have found everyone there to be extremely helpful, and we are the 3rd owner of our Krogen 39.
When you do get the specs, could you post them here on the forum so that I can record it for future reference. Ours is looking rusty, and who knows when it might fail.
All the best,