That yellow square Is a visualization of how Remington milled their solid and vent ribs integral with the barrel during the first fifty years of the 20th Century.
The Sportsman and the Model 31 Skeet Guns were introduced in the February 15, 1935, Remington Arms Co., Inc. catalog. From that time onward a SKEET choked barrel could be had on most any Model 11, Model 31 or Sportsman in addition to the Skeet Guns. Generally speaking a SKEET choked ribbed barrel on a Skeet Gun would have two beads while a SKEET choked barrel for any other gun would only have a front bead.
