An inkjet printer comprising: a printer body and a replaceable printhead cartridge, the printhead cartridge having a casing that supports a pagewidth printhead; the printer body having a cradle for holding the printhead cartridge in an operative position such that the pagewidth printhead is adjacent a paper path defined by the printer body; wherein, during insertion, the cradle and the casing interact to form an over centre mechanism whereby, the printhead cartridge rotates against a bias prior until reaching a balance point, after which it is biased to rotate into the operative position.