Ventilated rib. The DM Lefever SBT with a solid rib was introduced in 1905, the Baker with a ventilated rib in 1909. The 1909 Remington catalog listed a matted rib or a ventilated rib ($16) on the autoloading gun. The No. 525 Stevens Repeater with a "Hollow Matted Rib" was introduced in 1911.