They recommend 100 oz-in motors. For 1/2-10 5 start, you'll want 300oz motors. HobbyCNC sells those as well as the small ones. Another good screw choice would be 1/2-8 2 start. Not quite as fast, but plenty fast for a machine that size, and will give you a bit more force, and let you use slightly smaller motors. But I'd still recommend about 250oz in if using multi start screws. Also, on a machine that small, you can probably get away with 3/8" screws, which may be quite a bit cheaper.