(!!!) 6F8G National Union parallel dark gray plates 1950 era (11.2ma and 12.8ma)
6F8G RCA gray ribbed staggered plates NOS no printing 1950's (7ma/8ma)
6F8G RCA Radiotron staggered black ribbed plates used/good 1940's (8.2/9.6ma)
6F8G RCA Radiotron staggered black ribbed plates used/good 1940's (9.0/7.2ma)
6F8G Sylvania Zenith parallel black ribbed plates used/good 1940's (9.0/8.4ma)