A piston assembly having a piston (10) and a piston/piston rod coupling arrangement wherein the piston has a cavity (12) with a catch portion (15) and the piston rod (20) has a coupling member in form of deflectable flaps (23) for engagement with the catch portion (15) inside the cavity (12) of piston (10). The flaps (23) of the coupling member have a radially variable dimension which is biased radially outwardly by dedicated bias means (26) upon entry of the coupling member into the cavity (12) of the piston (10).
