Ah so. What you need is called a "feeler gauge".
You can buy them cheap, or expensive. The cheap ones work fine. You will also need a small slotted screwdriver and a small hex wrench to loosen the adjusting nut.
Here are some inexpensive tools that will do the job:
http://www.harborfreight.com/32-piec...uge-32214.html
http://www3.towerhobbies.com/cgi-bin/wti0001p?&I=LXHGC1