Hmm. I think this is a utility metals arm. The Hapco upsweep arms here have a similar mount but the cantilever arms here are different. It's like a flat plate that's bent so it touches the pole. The M-400A looks good on that arm.
I agree too, Michael, it closely matches the Utility Metals in the catalog....we have those in BGE only in 4 foot, we also have HAPCO which is very curved at I think 45 degree, it's rounded all the way and we have those in 4 foot as well
This one would be the "P" Series Cantilever