I have been packing up more of the collection -probably destined for the after hours auction 2024 (never too early to plan for that show). I found one U 1352 Canadian that is different. They look the same but one is obviously larger diameter and noticeably heavier. Flanked by a regular pair the smaller wire groove is also obvious Out of boredom and a little curiosity I probed further. The usual dia. measurement for this insulator is 3.75 inch- mine is 3 inch. this increase required almost 25% more material to manufacture. (450 vs 560 g. ) Barrett informs me this is likely an early production. A reduction in size would save considerable money for the company. If production dates were before and continued into the depression era, money was tight and so it's easy to jump to the conclusion that could be the cost saving reason.