7mm vs. 6mm

[laxer47]

What exactly is a 7mm gearbox and are they bad? What makes them different than a 6mm gearbox?

[Gcommando]

The mm determines the bushing size. A 7mm GB will only work with 7mm bushings/bearings. It's the same thing for 6mm, 8mm, and the occasional 9mm gearbox. People say that larger bushings are more durable (or something along those lines), but I don't think it'll make too much of a difference.