Here is a line of fence insulators made by Knox Porcelain Corp, Knoxville, TN. The white ones on the right are Knox brand. The ones on the left were made by Knox for Prime Mfg. Co. Miliwaulkee, WI. This includes a fence lightning arrester and a rare grounding rod with disconnect clamp to attach to the wire. They are marked PRIME. I have seen the blue one on a fence line before but would be pretty fancy for a fence on a farm. Maybe used as a marker on the line.