McVitie Weston valve collection, BTH valve, type R7
BTH valve, type R7, etched 5252B, (RMW/B75B - McVitie Weston number), by British Thomson-Houston Company Limited.
BTH valve, type R7, etched 5252B, (RMW/B75B - McVitie Weston number), by British Thomson-Houston Company Limited.