The National hive brood box for 21,5 cm frames.
Standard frames match with it. From the outside it's covered with spruce wainscot. Inside there is air dilatation and 2-centimeter styrofoam insulation, thanks to which bees can maintain their own microclimate. Within the National Beehive is finished by pine or spruce boards. Using a 3.2 cm wide Hoffman frame, 11 frames are insert.
Frames you can buy in diffrend offers.