Question: I just got a used Fender Starcaster S1 to compliment my existing Behringer strat.
Upon inspecting it, I noticed that it has different backs on it's tuning machines.
What are the differences between these besides appearance?

![enter image description here](https://i.stack.imgur.com/ewWNu.jpg)

Answer: 
Inside them both you have a cog and a worm gear, which works as per this gif from Wikipedia:

![enter image description here](https://i.stack.imgur.com/OkkUk.gif)

Worm gears have a very useful property - they can cope with high tension without slipping.

The casing differences are purely cosmetic.
There are some easily noticeable differences:

1. Tuners on Behringers are attached with screws on the back side, while the ones on Fenders have a nut on the front.
2. There might be differences in the string attachment itself (not pictured here).

Some differences are not as easily spotted, but are a huge deciding factor:

1. For example, **differences in gear ratio.** Generally, higher-end tuning machines have a **high ratio** for easy, minute adjustments in pitch.
2. In addition, **differences in build quality.** Lower-end tuners are less likely to hold their pitch, and may be more susceptible to damage from use.