Image shows the basic difference between these 4 dials (note: there are variations of these dials)
Thanks for posting this, John!
Also note that the the sides of the casings differ between the #6 and all earlier 3" dials. The #6 is also slightly taller.
As for non-WE dials, here are a dozen various different manufacturer's dials that may be helpful in identifying that dial you got your hands on.
thanks to another forum member - Gary
==========
#1 S-C
#2 KELLOGG For RED BAR 10D
#3 KELLOGG For SELECT-O-PHONE 11A
#4 KELLOGG 15G LD590
#5 AE
#6 SIEMENS NIG
#7 FEDERAL ELECTRIC
#9 AE JF45 820C
#10 AE 820C
#11 NORTH ELECTRIC 941
#12 AE 870C AE8
#13 S-C 247