I just found this today with my dad along the Niagara-Toronto Transmission Line. I noticed some of the towers were unfortunately torn down. The insulator was found lying upside down near a former tower. It is marked "A.F.". If anyone has more information about the insulator (date of manufacture, value, A.F.), I would be grateful. Thank you.

Ted Wilush replied:

Hey Paul,

Your insulator is a Canadian Porcelain M-3733 and was used en-mass on the old T-N line as replacements for the original M-3740s, installation would be mid 1920's. The A.F. marking is a mystery and is also found on a number of other CP multipart styles manufactured around the same time. Interestingly CP very rarely marked their larger insulators with their name during this period.

Thanks Ted!