OK, here's the problem with using SG shaft engines from 4-wheelers. You might be able to find a flex cable collet that will thread on but once you put a spacer and flywheel on there aren't many threads sticking out. I wouldn't try the 5mm FE collet unless there is a flat spot ground on the shaft so that it doesn't spin. I've got a buddy that tried cutting a SG shaft down on an OS .12 and the results weren't good. At the bottom of the lake are 2 flywheels, flex cables, props and collets, half of which were mine.