Wow I wouldn't buy a combine without a rocktrap. Cheap insurance. Anyway remember to dump it every few days to keep the stuff soft. Corn isn't real bad because you don't pick up alot of rocks, but beans however are a different story. If it gets hard the rock might not be able to go in plus it empties any rocks out. The corn ears will get jammed in there prety tight if let go a long while. See the beater drives the rocks into the trap.