Hy-Vent Identification Help

Hi Everyone,

I'm a little embarrassed to ask this question but I really don't know what the size it is.

My Taco Hy-Vent has been leaking for the past couple of years (I know, I know) and went down to the local Home Depot and picked up a replacement Taco Hy-Vent. I never got around to installing it because I forgot about it, but I did notice it was "fatter" than the one I currently had.

Two weeks ago we had the annual boiler service from our oil company that includes a nozzle, filter and whatever else they do. I pointed out to the technician that I needed to replace the Hy-Vent because it was leaking. After the technician left I saw he changed the Hy-Vent for me. I wish I knew prior because I would have thanked him.

My question is what size did he put on? The old "leaky" one was the "slim" version and that's what he replaced it with. I want to make sure so I don't buy the incorrect "fat" one again.
I'm not even sure the one I bought was the correct thread size because I never got around to installing it. ANY IDEAS? Thanks in advance for trying to help me out.

The "Slim" new one, which matched my original.




A side-by-side of the "fatter" Home Depot one.