Lastly here is patent US3,061,667 showing the R-3, R-4 or R-5 and the RC-1. Beside it is a catalog advertisement for Continental Rubber and there locations. Note down in the left hand corner it has companies in Mexico which is where the R-4 Hecho En Mexico piece was made. I'd like to find one of these and the R-4 style that has 8 0 (1980?) on top instead of R-4. I think this was one of the last runs of this style before the company closed. If you have any other info or insulators I'm looking for please let me know. Hope you enjoyed the posts. Take care to all.