6.0" diameter, 4.0" high. Inside machined to fit G-11 and GM-8 mounts. Tube has 1/2" thick bottom with 1/2" hole in center, posts for the electronics are mounted on the side. Also used on top of permanent piers.
I've threaded so that the Meade bolt screws directly into the Adapter. I've only mounted for a week or so, bought a specialized tripod, so I no longer need this adapter. Very minor bolt marks where G11 mated to the adapter otherwise perfect.
Cost $79 new plus shipping. $60 shipped CONUS.
Call if you have any questions.