Pictured above are a few varieties of 1932-34 Model B and Model 46 ammeters. The two lower ones are both 20 amp 1932 styles. One is chrome bezel, and the other black. The black one may have been for service or for commercial.
The two upper ammeters are both 1933-34 style inductive ones. The one on the left is a 20 amp with chrome bezel, and the one on the right is an NOS 30 amp Model 46 gauge with black bezel.
The pic above shows the backside of the above ammeters. The two lower ones are 1932 with the wire terminals. The two upper ones are 1933 and 1934 Model 46 and commercial which use the inductive wire loop. The NOS 30 amp gauge is on the top right, and note that it has a larger loop to pass a larger size wire through.