Michal didn't put 9 and 10 because he didn't want people making overly retarded weapon mods. A good bit of what Grimreck said was wrong, so let me clarify.
2, grenades: Not like normal grenades. They can take more than 3 seconds to explode.
11, knife, chainsaw: Shoots the invisible things that chainsaws/stabbing knives expel to cause damage.
13, knife: shoots knives, somewhat like what throwing the knife does.
Edit: It is very easy to change a weapon's size. Just make the image bigger.