The present invention provides a piston washer (1, 51) for a drug delivery device, the piston washer (1, 51) comprising a central portion (2, 72) arranged about a centre axis, a peripheral portion (3, 73), and an axially pliable structure (8, 78) connecting the central portion (2, 72) and the peripheral portion (3, 73). The axially pliable structure (8, 78) is preconfigured to undergo permanent deformation in response to a difference between a first resultant force acting on the peripheral portion (3, 73) and a second resultant force acting on the central portion (2, 72) exceeding a threshold level. The piston washer (1, 51) is configured to transition permanently by deformation of the axially pliable structure (8, 78) from a first state in which the central portion (2, 72) and the peripheral portion (3, 73) are physically connected and assume a first relative axial position to a second state in which the central portion (2, 72) and the peripheral portion (3, 73) are physically connected and assume a second relative axial position in response to the difference between the first resultant force and the second resultant force transiently exceeding the threshold level.

Claims data not available