Which pulley to purchase?

If you look in my post history, I bought a cheap Prius a while back with a blown engine and swapped in a good used one. I had bought that one to resell and have since sold it. I came across a 2006 that needed a transmission and decided I'd buy this one for a daily driver. Got that replaced a couple weeks ago and running good!

I noticed when working on it that the engine coolant was a little low. Further inspection revealed that the water pump had some pink coolant crust around it. I ordered a new water pump and belt. What I'm having trouble finding a good answer on is which idler (tensioner?) pulley to order for a replacement while I'm in there. I know there is only one to replace, but rockauto and amazon seem to list two different types (idler and tensioner) along with slightly different sizes. I thought the idler pulley *was* the tensioner pulley by adjusting the bolt on top? Any insight on this? Thanks!

 

What threw me was even though they’re aftermarket parts with different names, they also had different sizes listed. That part number is exactly what I was looking for, thank you!