I was going to build a rocket capable of handling F & G motors. However, the site that I normally use does not have seem to have the parts I would need. They do have an engine hook (I prefer this retention system for smaller rockets), they do sell the engines as well, I found a motor tube on another site, but I am not sure where I could get some centering rings from. The rocket would have a tube size of BT-60 or BT-80. Any ideas? Or does the hobbling motor mount for D+E motors hold Fs?