Duplicate tags: 2-stroke and two-stroke
Edit: Also 4-stroke and four-stroke
two-stroke has 1 follower and 22 questions, and 2-stroke has no followers, and 9 questions. They seem to be pretty obviously the same thing.
I think we should go with two-stroke, as it is (slightly) more common. Also, (IMO) it flows a little better. The same would also go for 4-stroke and four-stroke, although which one is again completely aesthetics.