Duplo Brick 2 x 2 x 2 with Vertical Grooves

Reference

41978

Duplo Brick 2 x 2 x 2 with Vertical Grooves (part 41978) is a LEGO element. CollectORbuild's catalog records it in 23 sets, including Around-The-House Set and Black Castle. It has been produced in 4 different colors.