Here's what I found forestroke. I measured the diameter of the threaded portion of the long screw that goes through the .32SX muffler. It's 3mm. The .46 looks like 3.5. The .91 is bigger yet, probably 4mm. I didn't pull the long screw out so I could measure the thread pitch (too lazy). Your local auto suppy might have small metric nuts. If you can't get a 3mm lock nut, double nut it with plain old hex nuts. Clam's all-thread method would work well too.