Actually, after posting my comment I went to test it and found out that the torus at default of 256 was 1% smaller than the cylinder. As for changing the number, the outside diameter stays the same and the inside grows larger with a lower number. ie, if you make a torus of 100, its the same outside, and larger hole. Apply the correction factor if you need. Experiment. Remember, Bryce isn't a modeler, that's what other programs are for. (a good freeware is metasequoia http://www1.sphere.ne.jp/mizno/main_e.html which has export capability in the LE freeware versions) Good luck, hope this helps.