These are a new kind of 25mm round base that has been designed to work with figures that have either an integral “puddle” base or flat feet. One side has a 23mm x 1mm indented recess so that figures with puddle bases will have their feet flush with the edge and eliminate that “standing on a hill” look.
The other side is flat for figures which will have their feet glued directly to the base. These bases have a low 2mm profile to blend well with the tabletop and there is also a 3mm x 1mm hole to add a magnet for secure storage or for use with a movement tray.
This is one sprue of 25mm round bases, 12 bases in total.