Wish I could find neat stuff like this in California. This Chubbuck corner bracket was found in Upper Black Eddy, PA. The iron bracket came with the original Brookfield pony insulator. It is marked on the arm Chubbuck 20/ PAT SEPT 9 90, which corresponds to Eugene Chubbuck's utility patent #436,120 granted on September 9, 1890 for a split thread insulator pin design.
See the ICON patent library at: http://reference.insulators.info/patents/detail/?patent=U436120
See the next photo for the patented design feature [id=429973654]