Around 1850, maybe at the very end of the 1840's, Charles V. Walker designed the insulator in the photo. It was shaped like a hourglass, and the design was to minimize the contact with the wire. Like the Cooke insulator, it was mounted to a flat piece of wood with an U-shaped iron clamp. As for their insulating properties, they worked very well but thanks to their delicate design they were liable to breaking. And as with the Cooke insulator, the wire had to be cut and thread thru the replacement insulator.