Shank is the correct name for the part you need.
You didnt' say how much rise/drop your current shank can handle. It's measured in inches. If you have the shortest one, it's probably this one which is a 6 3/4" shank.
Do you currently have it assembled with the shank pointed down as in the picture? If not, the thing is reversible and that should give you plenty of drop.
If it is already dropped as low as it can go, then you likely will need something like this:
Any RV dealer or trailer shop should be able to help you get the right shank. Generally it is a stock item. Or you can buy online from www.etrailer.com
to help you look over what is available. Click the Products link and then select Weight Distribution and then WD shanks.
They run between $100 and $125 new. Add shipping costs if purchased online.
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