3.What's the diameter of F9's conduit?

A: It's maximum diameter is 6.0mm. It's recommended to choose 5.0mm eartip if you're planning to buy foam eartip and choose 3.5-5.0mm eartip if you're planning to buy silicone eartip. Theoretically, the smaller the aperture of the eartip is, the more bass you could get, and the larger the aperture is, the better pitch you could get. PS: For reference only.