By way of explanation, the ratio is how many times you have to turn the knob to make the post turn one full rotation. So with 14:1, it takes 14 turns of the knob to make the post go around once. The higher the ratio, the easier it is to tune with precision because the amount you turn the knob results in less movement of the post, allowing for more accurate control of the string tension and hence more accurate tuning.
The size of the tuner and the gear ratio are completely unrelated. You should be able to find a technical drawing of the tuners somewhere that detail the dimensions of the post and hence the size hole you need to mount it. If you know exactly the brand and model of the tuners in question, you should be able to look up the specs either on the manufacturer's site or on a site that sells them like Warmoth or Stewmac. Barring that, try a google search. That being said, I wouldn't buy anything from that particular seller just on principle. I don't like people who can't admit they don't know something and give wrong info instead.
