I have a Vixen Porta II Alt-Az mount that came with a tripod. The mount head works well, but the tripod is not nearly stable enough for use with my 15+ pound Comet Hunter Mak-Newt. I have a heavy duty tripod that I would like to use, so I'm thinking of getting the Vixen 3942 tripod adapter. The adapter has a 1/4" screw hole, and the heavy duty tripod has a 3/8" screw, so I could get a 3/8"-16 female to 1/4"-20 male adapter, but I'm not sure if that would be stable enough since the adapters I've looked up have a much smaller diameter than the top of the tripod and the mount head.
Also, I thought I read somewhere that there are three bolts that attach the adapter to the tripod head, but the head I have did not come with any bolts; the tripod that came with it attaches with one large screw with a tightening knob. Does anyone have experience with attaching this particular head to a tripod that has a 3/8" screw? Do you need to use 3 bolts as well as the 1/4" to 3/8" adapter, and would such a screw size adapter be stable?