Beldar is correct; I was sloppy in my earlier response. I just re-measured mine.
My 'heavy air' sheet is 5/16"; my 'regular' one is 1/4" in diameter. Take your pick
Not necessarily. If the block size doesn't increase as well, thicker line increases friction, which in turn increases the load in your sheet hand. It's the same the other way: I was able to quit using gloves when I changed my Laser sheet from 8 to 6 mm. This is especially relevant in the Sunfish, as the sheet blocks are those tiny Racelite things.