Use the antenna on a Vectra C Caravan. Need there the M5 thread. The thread adapter is far too long. The antenna is then not properly. Have the thread then cut with a hacksaw (-> mother to thread for a straight cut and a clean thread). In addition, the M6 side with Loctite is recommended to use. The reception performance is unchanged compared to the orig. Opel's antenna which 4 cm longer.