Neither of these two engines is ringed. The OS is ABN (Aluminum piston,with a Nickle Brass cylinder) and the Tower is ABC (Aluminum piston, Brass liner w/ Chrome plating)

Both engines have a ball bearing supported crankshaft.

I vote for the OS because of my positive experience with their engines. Good quality and easy to operate. I have never owned a Tower engine so if you do a search on Tower in the glow engine forum you will know as much about them as I do. Maybe more.

Eric