[Thomasr]

I've seen some pretty outrageous looking cables, but don't have examples on hand to actually measure.

If I were designing a hole that a headphone cable would have to pass through, what's the maximum diameter I should consider?

(just the cable - I'm ignoring the size of the connectors for now)

 

[warrenpchi]

Ignoring the crazy custom cables that some of us might have (I once commissioned a headphone cable made from a length of audiophile speaker cable), I believe the "thickest" headphone cables currently in production are from Viking Weave.

I can't give you actual dimensions because (a) I don't have any of their cables; and (b) their non-constant diameters may vary slightly depending on which part of the braid you're measuring.

I would just go ahead and contact them to find out more. Good luck!