The last twister I made was using a 6" fabric square and the custom twister square was 4-1/4", I found when I was using my rotery cutter that I was over cutting and going into the next square space....so until I really got my sea-legs on this project, I ended up tracing around several blocks with a pencil first, then cut out with rotery cutter. I also can not stress strongly enough the importance of keeping your blocks in order, otherwise you are going to have one heck of a puzzle when you are done (ask me how I know!!!) If you have a planning board this is when to use it....This is my last twister, it was done a little different from others I have seen with a white block between each color block...just gives a different look....
http://www.quiltingboard.com/picture...s-t201571.html