We used one of these on the farm in the 1930s. It is a windrow
attachment and is attached to the sickle bar of a mower. We always
called them “pea rollers.” I assume they were designed to windrow
peas when cut with a mower. We used them when cutting alfalfa or
clover for seed. They would gently roll the foliage into a windrow,
thus saving seed as compared to using a side rake.
– Bob Schink via e-mail