Does your operators manual show removing the two 1/4-28x 1/2 bolts and greasing the casters?
SAE thread grease fittings are 1/4-28 thread and this is what you posted in the Amazon link.
I'm not sure why Ferris installed a 1/2" long bolt there on page 4, item 25. Some companies install a small plug the is removed to install a grease fitting for lubing and then remove the grease fitting and reinstall the plug.
Before removing the bolt, I would make sure that this is a lube point as the bolt may be holding a part in place.
There is intentional drag built into the caster steering to prevent them from loosely swinging during machine operation, item 21 are cupped washers installed back to back and when all parts are fully assembled, they provide tension by pushing on the roller bearings increasing the drag on them.
Item 24 are two tapered bearing cups that the tapered roller bearings roll in, these cups are the first parts to be installed into the caster steering support sleeve. The bolt, item 25 may separate these cups and position them in the sleeve.
I'm not familiar with your machine or any Ferris machine, just judging the parts as shown in the manual and 55 years as a mech.
