Cap assembly to be used with a medicament delivery device, which medicament delivery device comprises a housing and a medicament container holder, said cap assembly comprising - a retainer member connectable to the medicament container holder, - a hub comprising a needle having a proximal end and a distal end, said hub being arranged with threads, which threads are arranged to interact with corresponding threads on said retainer member such that said hub is coaxially movable within the retainer member, - a removable inner cap arranged outside and coaxial with said hub, which inner cap is arranged with threads, which threads are arranged to interact with corresponding threads on said retainer member, that said inner cap and said hub are arranged with cooperating slits and ribs configured to rotationally lock said hub with said inner cap but to allow relative sliding between the hub and the inner cap, - a removable outer cap being coaxially arranged to the inner cap, and - a cap clutch mechanism comprising a locking member which is axially movable but rotationally locked in relation to said inner cap, that said locking member is arranged with first engagement members and that said outer cap is arranged with second engagement members arranged to interact with said first engagement members; in that said locking member is axially movable between a disengaged position in which said first and second engagement members are out of engagement, wherein said outer cap is rotatable in relation to said inner cap, and an engaged position in which said first and said second engagement members are engaging each other, wherein said outer cap is rotationally locked to the inner cap; characterised in that the cap clutch mechanism further comprises clutch biasing means arranged between the outer cap and the locking member, said clutch biasing means being capable of biasing the locking member for keeping it in the disengaged position. - a retainer member connectable to the medicament container holder, - a hub comprising a needle having a proximal end and a distal end, said hub being arranged with threads, which threads are arranged to interact with corresponding threads on said retainer member such that said hub is coaxially movable within the retainer member, - a removable inner cap arranged outside and coaxial with said hub, which inner cap is arranged with threads, which threads are arranged to interact with corresponding threads on said retainer member, that said inner cap and said hub are arranged with cooperating slits and ribs configured to rotationally lock said hub with said inner cap but to allow relative sliding between the hub and the inner cap, - a removable outer cap being coaxially arranged to the inner cap, and - a cap clutch mechanism comprising a locking member which is axially movable but rotationally locked in relation to said inner cap, that said locking member is arranged with first engagement members and that said outer cap is arranged with second engagement members arranged to interact with said first engagement members; in that said locking member is axially movable between a disengaged position in which said first and second engagement members are out of engagement, wherein said outer cap is rotatable in relation to said inner cap, and an engaged position in which said first and said second engagement members are engaging each other, wherein said outer cap is rotationally locked to the inner cap;