The Dx/Sx sides have the interlocking millings in the front wall. The front and back walls,have the interlocking millings for the Dx/Sx sides. For attachment to the bottom,there is no milling
SPACER SAVES BEES AND MANIA depending on how it is mounted in the Beehive, flush milled classic method, or higher than 6.5 mm "save bee space" method, allows the bees to have two passages, one under the honeycomb head, and the second, between the side of the honeycomb and the wall of the Beehive. The rounded edges of the spacer,avoid offending the beekeeper's hands .