refinished american industrial antiquated mottled reddish-brown glazed ceramic transmission line insulators possibly fabricated by or or the clark electric & manufacturing co., new york city, ny. the medium-sized porcelain insulators units were salvaged from the interior of an old chicago factory that specialized in the fabrication of transmission drives, friction clutch pulleys and other heavy machinery. the insulator units contain cast iron perforated bracket hoods with large eye hooks affixed to the undersides. the two insulators were still being used with a very high voltage electric system requiring this type of insulator. the first electrical systems to make use of insulators were telegraph lines; direct attachment of wires to wooden poles was found to give very poor results, especially during damp weather. the first glass insulators used in large quantities had an unthreaded pinhole. these pieces of glass were positioned on a tapered wooden pin, vertically extending upwards from the pole's crossarm (commonly only two insulators to a pole and maybe one on top of the pole itself). natural contraction and expansion of the wires tied to these "threadless insulators" resulted in insulators unseating from their pins, requiring manual reseating. the first to produce ceramic insulators were companies in the united kingdom, with stiff and doulton using stoneware from the mid 1840's, joseph bourne (later renamed denby) producing them from around 1860 and bullers from 1868. utility patent number 48,906 was granted to louis a. cauvet on july 25, 1865 for a process to produce insulators with a threaded pinhole. to this day, pin-type insulators still have threaded pinholes. the cast iron components have been brushed down to bare metal and sealed with a clear coat lacquer. priced for the pair. measures 6 inches in diameter 6 inches in height.