Can someone explain me what is the difference between Robos type monorails exten sion and G series and help identify the part number of an extension tube? I need a 25cm (10") extension tube, male and M6 screw one end, fixed rotating kn ob the other end. Would this be a G serie? Or is it an older make? It seems that the current models have female/screw one end and an inner screwing device accep ting other extensions the other end. I'm also mixed up by the different manufact urer numbers provided by Toyo USA and Toyo Intl. Thanks for your help!