I've only come across a handful of intact grey, unmarked Thomas M-2255s around here in the 20+ years I've been collecting. This, despite their having once been used in large numbers on first-generation Hydro Electric Power Commission distribution lines in the area.

When I spotted it [id=725450384;in a bin full of junction boxes and other assorted modern electrical supplies] I was pretty excited!

This example is an especially nice one of these in a few ways. It has a darker-than-average greenish grey glaze and all-original cement. The crown is crudely trimmed so that the side groove is pretty lop-sided. Some remnants of the original cloth-covered tie wire are still stuck to the crown on one side which really appeals to my "keep it as found" collecting mentality. The underside of the top shell is marked with the sort of "X" incuse that some Thomas products have. To top it off, it's in excellent condition with just a few pecks and scuffs on the crown.

I nearly drove by the shop I found this one in as it just doesn't stand out as a "likely" place to find something. I suppose you only reap what you sow - so go check that spot you haven't visited for a while and you may just find something great.