CD 135
CHICAGO INSULATING CO.
[020] (Upper shoulder) CHI.INS.CO. PAT.OCT. 16. 1883 (F-Skirt) [Glass dots may be present] SBBlue . . . . . . . . . . . . . . . $75-100
The Chicago diamond groove. The strange cutouts around the wire groove were designed to reduce the contact with the tie wire.