There are two constructions of summaron 35's, the first looks like a collapsed elmar and has a 36mm front ring, they are all screw thread fitting.
The second construction is predominently bayonet fit and look like a summicron 35f2, these have a 42mm front ring the same as summicrons.
I think lee has purchased the first type, and the correct hood is like Joe's.
All the other hoods mentioned, itooy, irooa, 12585, etc fit the later 42mm front, and won't fit the small front.