Collectors name several causes: manufacturing tolerances on the thread, an accidentally swapped cap or worn thread teeth through daily screwing, occasionally also through too firm tightening by third parties. Between barrel and cap, in final inspection, no play should occur; an audible crunching with light wobbling indicates a no longer matching thread. Self-help (e.g. warming) is advised against, since the thread is anyway not used for slip mounting. Sending in to Montblanc service is recommended; in warranty cases the cap is generally completely exchanged.