The insulator in question is second from the right, and as luck would have it there is no embossing to help me figure out what it is.

I went down to the local antique store today and found an unusual insulator. It's like a CD 133.1 but a little taller and chunkier. Maybe just a chunky CD 133? It measures 3'' across the base and 4 1/8'' tall. Its mold line is unusual too. It goes up the side of the insulator past the wire groove and goes around the top of the dome (near where the threads end). Its dome is also a little concave looking. There is a small dot at the top of the pin hole and the pin hole is somewhat more narrow? (it won't screw down onto a standard peg, maybe a factory mess up?)

Update: Turns out this piece is a CD 133 No Embossing [025] {DEC 19, 1871 Patent style}

I got conned into paying $15 for it. Can somebody help me identify this piece? (click next for more pics)