Wanted: Someone with several different sizes of cotter pin.

just putting the pin in and tightening the nut is a bad idea, in order to get it tight enough to actually hold your cranks in place you'd just strip the thread. you should:

1. put one cotter through the crank
   
2. tap it into place
   
3. if it doesn't fit quite all the way through remove it with one hard tap from the other side and file it a little
   
4. try again, if it still doesn't fit repeat 3.
   
5. when it finally does fit right you'll need to twat it hard to settle it in place, then tighten the nut, spanner-tight
   
6. fit the other in the same way, from the opposite direction
   
7. after 2 weeks they'll probably come a little loose, as soon as this happens wallop the pins *then * tighten the nut, they'll probably last you a good 25 years if fitted properly!