The style I have at work has a rubber plug that is inserted into the tubing and expands as you tighten a bolt on the caster base. Yours seems to be missing the bolt head.
They just drive out. They're on a plastic insert that wedges into tube. They hold the tray on too. Mine used to pull out if I left tools on tray and picked the seat up, glued them in with RTV.
They just drive out. They're on a plastic insert that wedges into tube. They hold the tray on too. Mine used to pull out if I left tools on tray and picked the seat up, glued them in with RTV.