Shown are three, 50 amp watt hour meters. The top meter is a Westinghouse Type-OB with the larger terminal chamber, 115 to 230 volt. Bottom left is a GE I-14 with a larger terminal chamber to handle heavier loads, 110 volt. Bottom right is a Westinghouse Type-OA, 100 to 200 volt / 50 amp rating. The entire meter's case is slightly larger to accommodate the larger current coils.