The first item, Walbro Wa 167 is the standard of comparison for 11 mm carbs for use on weed whackers. I have several of them.

$35 is a lot better price than going to the lawn mower shop or buying one from horizon.

You are correct, the other carbs are 1/2" venturi carbs and are too big for the usual Ryobi 31. But the Wa 167 is a perfect carb for your engine. It is what I have on my Ryobi.

There is another post, close to this one, where I put all the Walbro carb models that are the size you want. Copy the list. If you look around, you may find one of these models for $10 on a auction site?

Enjoy,

Jim