Question about the motor mounts...

So I need new motor mounts. I am not sure EXACTLY which I need. But i have decided I will just replace them all. Anyways, my question to you all is this, why is it that when I was shopping around online for the best priced mounts, I found that nearly all the mounts have different dimensions, but are listed as being the same part? For instance, I found a front lower mount from two different companies, one from Westar and the other DEA. When I was looking at the specifications, the dimensions were slightly different. You might be thinking, ok this guy is a retard, he clearly was looking at different mounts, but I'm telling you the pictures were exactly identical, the parts were the same, just made by different companies. I noticed the same thing with another Westar mount and an OES Genuine mount. The dimensions were different.

Now, I'm not exactly a car expert, but this just doesn't add up to me. Anyone got any clue why this is? And also, should I even be looking into buying a mount from Westar, DEA, Anchor, etc, or strictly the OES Genuine mounts? Thanks.