This is a Green Stuff World Plastic Rectangular Base 25x50mm (10pcs)

Set of rectangular plastic bases, due to their compatibility they are ideal for use with traditional Warhammer cavalry units, as well as in other types of wargames or miniatures role-playing games.

The back of these cavalry bases have 2 covered slots so you can open them and insert figures that have supports on the feet that need this type of coupling.