Bob, the 660 series were never catalogued, that we know of, which is what makes the sizes so hard to determine. It’s possible they followed the same sizes as the regular ones...or not, hard to tell without catalog information or someone’s really large collection.
They seem to be less common than the regular PH ones. For those who are interested, I below listed the 660 patent, and the regular SD patent second.
No. 1,677,572 on July 17, 1928 by L.V. Walkley
No. 1,170,709 on February 8, 1916 by W.S. Thomson
Mike