These are two insulators manufactured by the Locke Insulator Mfg. Co. These have "Insert type" metal crowns (the metal crown is a seperate piece that's inserted into the insulator). This was to combat RFI (Radio Frequency Interference). The multipart styles that sport this unusual and neat feature are: M-2343, M-2639, M-2770, M-2961, M-3650, M-4343. Locke also cataloged applied metal crowns, as can been seen on styles: M-2324 & M-2620A. (If I have missed any styles, please send me a note)