Helmet on left is unmarked Pittsburg with typical un-glazed pin hole, picture on right shows glazed pin hole, but neither have inner skirt. Is the one on the right a Pittsburg product ? As always any help appreciated. Thanks to Dan Ling, Bob Stahr, and Robin Harrison for their responses. Insulator was probably made by LOCKE or Lima not a Pittsburg. Just got this info from Elton: The one on the right was made by Locke in the early 1910's. Most have the incuse VICTOR on the skirt.