There are no "standard" screws used to mount motors (although from a CD player, it's likely you're dealing with a metric size) - you're just going to have to find a way to measure them. It shouldn't be all that hard, with a cheap pair of calipers (your best bet) or even a 6 inch steel scale. You should be able to pick either up for under $10. You can determine thread pitch by using a pitch gauge (maybe $3 for a Chinese-made one) If your budget won't allow for buying new tools, take the screw to a good hardware store close to your home, and see what nut will easily thread onto the screw you have. That will tell you the screw size and thread pitch - and you can pick up longer screws while you're there.