I put the rail buttons in the centering rings, so however far apart the rings are is how far apart the rail buttons are. I would say mine are usually 10"-17" apart, depending on the design of the rocket. As for parachutes, I get a lot of mine from rocketchutes.com. Very fast shipping, great prices, and lots of color choices.
Ok I will keep that in mind. The screws just seemed a little short, I got the well nuts and they hardly thread into them without a tube thinkness included. I'm sure they will be ok, I'm just a little paranoid. If not I can drill the buttons out a little so the head of the screw goes in a little more(I tried to explain that as understanding as I could)..thanks, for your time, I know you have your own things to deal with besides me asking you questions all day.. Mike B.