Hello, did you try to hold the stem and to loosen the nut with a wrench? Sounds like that may do the trick if we understand the situation correctly.

came here for same thing (i think?). bought a pack of 2 and the socket and stem are already joined. instructions say after drilling the hole (step 1) "2. remove the socket from stem and insert it into the drilled hole by tapping with hammer. 3. push caster stem until it locks." but it's already locked and i can't seem to separate it. not sure how else to explain other than to say it's this exact one, and in the pack of 4, the parts are already attached like the pic shows. apologies for the 'greenness' of my comment. new to this stuff (obvi lol). www.shelllumber.com/prosource-caster-hooded-stem-2in-brass.html?feed=Froogle&gclid=Cj0KCQjwsqmEBhDiARIsANV8H3ZAUC9Hco_3bs_dZJ5ZBJRjKkCSeB5HPDQnfNOQWmcZz73EHb3EWGYaArmfEALw_wcB

Hey Leonitas, we've got a ton of casters on our site, and you can contact us by phone at any time--number is on our site. casterconnection.com/ Hope that helps!