How to lock casters?

[nursemom]

DH and I just put together our new Ragazzi crib (Cooperton series, model # 4401 in Antico White) and we love it.... but we can't figure out how to lock the casters. The nursery has hardwood floors, and it doesn't take much effort to move the crib. One little tot jumping up and down or rattling the sides might send the whole thing across the room! The casters on this model are ball type (like a ballpoint pen) and are mounted within the turned feet of the crib.

Can anyone help?

[HallsofVA]

Sounds like this may not work for your crib, given the description above, but it seems like many folks just take/leave the casters off if you don't want to roll it around. You could put something under the legs to keep from scratching the hardwood floors.