The gray M-2618a is a rather scarce insulator that was used on two lines historically. One line ran from the old Dryden, Wa. Powerhouse (long gone) to Wenatchee, Wa. that was built in 1906. The other installation was in the Portland, OR area on one of the interurban trolley lines there . Both lines used gray porcelain pin bases . another known find of these was in southern Utah near St George on a short line built with recycled materials during WW2 . Where the damaged specimens found in Utah came from originally is a mystery . As far as I know no gray porcelain pin bases have ever been reported .other then those used with the M-2618a . I have actually owned this insulator for many decades I got it in the early 1980's !