XPR Concave System. The BEST money you will EVER spend on your combine. Did you know every rotor combine loses 3-5 bu/acre? That’s $30,000 on the ground, year-after-year, on 1,000 acres of soybeans. But there is good news with our XPR Threshing / Separating Concave System – #1 Concave System for John Deere & Case IH combines. Exclusively Sold Here (i.e. no dealers).