Still using the 32 x 54 Jaw Crusher example, the top size of the feed entering the crushing chamber has to follow the F80 rule that 80% of the top size feed material is smaller than the gape opening. Using the F80 rule with the 32 x 54 Jaw Crusher, the 32" gape opening equals a 26" top sized feed, and with the 6:1 ratio of reduction, the ...