I know that these are some of the most common insulators around but I find the variances in them to be interesting. I've lined up 5 from my collection to show the differences in their dome shapes. On the left is what I would call a regular Hemi 40 dome. Next dome has very little "flair" or "lip" where the dome meets the upper WG lip. It is shaped crudely. Next has a little more "flair". 4th from the left is what I saw Brad Dahlquist call a "Hemi 41" with a normal Hemi 40 married to a Hemi 42 dome. Last is the square dome similar to the Brookfield CD 152's. I'm sure i'm not reporting anything new here but it's just interesting to think about what was happening in the factories so long ago and how these differences came to be. Thanks for looking.