Old Hay Loft Roller?

I found this on top of a barn beam up in the hayloft of a 100 yr old plus barn. It is about 40" long has metal dowel pins on each end that go inside a block on each end. The roller is about 4" diameter it was nailed to the top side of a beam in the hay loft with about a 3/4" gap between the roller and beam spins very nice. Was looking for any information on what this is and what it may have been used for. Thanks