50C deck drive belt is 1/2" X 85.5"
I just looked one up for myself. Seriously, you can look up your own parts.
Go to cubcadet.com, or partstree.com. Put in the model of tractor you are working on. Under attachments, choose the deck model. Look at the relevant picture associated with the section of parts you need.
Here is a link for the deck on both the Cub look up site, and partstree.com
Cub Cadet
Partstree
Now, you have part numbers and sizes. Take it from there.