BILLY Height extension unit, birch veneer, 32x11x14" - IKEA
Building A 1600sq Inch Hamster Cage | The Billy XL / The Petri Dish - YouTube
BILLY Height extension unit, white, 32x11x14" - IKEA
IKEA Billy Cage | hamsters
DIY Hamster Cage | Double Billy Cage (Read Description Below Before Building) - YouTube
Billy height extensions stacked. : r/ikeahacks
Why would there be an extension option for the tall BILLY but not the short one? I bought the extension in the clearance section, already assembled, so no hardware came with it.
BILLY Height extension unit, white, 16x11x14" - IKEA