Small (95 a) and large (130a) 3G Frame. The one on the left is the smaller frame with 4 holes highlighted in red where the larger frame on the right has 2 holes highlighted in the red.

4G’s have a typically black metal cover on the back. All others are aluminum.

This is a 6G large frame (135a). Note the gray pastic bearing cap and the bolts measure 5 3/8 in. center to center

This is the 6G small frame (110a) Notice the gray plastic bearing cap. The bolts measure 4 3/4 in. from bolt to bolt