Pictured here are two Prism insulators with the wide umbrella, in different sizes. I was a bit stumped as to the proper CD number for the piece on the right.

The piece on the left is:

CD 333 Prism [020] ... 7 1/2"w x 5 1/2"h (per price guide)

I had assumed the piece on the right was:

CD 315 [020]... 5"w x 3 7/8"h (per price guide)

It turns out it's a CD 321.

There are two distinct mold variations for this CD. The new 2011 Price Guide has a new appendix: "Insulator Style Variations Within a CD Number." Appendix VIII pg 11 shows the two styles of CD 321 side by side.

The two styles look quite different to me (more than just size). The primary drawing of a 321 has a pronounced semi-circular dip in the upper wire groove ridge (under each end of the saddle groove). Style A" has a horizontal wire ridge. I think Style A looks exactly like a CD 315 and 333, sized in between. Still, it's nice to know the consensus is that it's a 321.