Edwin Clarke was an engineer at the Electric Telegraph Company in England. In 1850 he designed an insulator to replace the Cooke and Walker designs. It was designed to be bolted under the crossarm. A threaded spindle was fastened with lead in the insulator, and the insulator was protected by a cap of zinc.

The photo shows two Clarke insulators marked "REID 1851" with their zinc covers attached. Both have a hole thru the head, so also with these the wire had to be drawn thru all insulators upon installation.