6 1/2" X 5 1/2" (163mm X 140mm)

(inside front skirt)  KШ–10Д   

(inside rear skirt) ШС–10–А  

Picture courtesy Darryl Wagner

6 5/8" X 6 1/8" (166mm X 156mm)

No markings

Picture courtesy Bob Berry

6 5/8" X 6 1/8" (166mm X 156mm)

No markings

Picture courtesy Aleksandr Chabatkou

6 5/8" X 6 1/8" (166mm X 156mm)

No markings

Picture courtesy Aleksandr Chabatkou