Just finished up a new cable for my Sennheiser HD650's inspired by the CMYK colorcode   26 awg silver coated copper individually braided in type II paracord. Neutrik NYS228BG 6.3mm headphone jack to a Qables Y-Splitter with Acrolink Sennheiser ends.       

  Although I use paracord instead of Multi filament sleeving to do this, with a 26 AWG wire type III paracord (550 LB, diameter 10/64") is way too bulky but it will work, type 1 paracord (microcord, diameter 1/20") can work but its absolutely miserable and near impossible to thread the wire...

550 Paracord has a diameter of 5/32 inch which is 3.96~ mm. In theory 8.5mm should be large enough.

*edited for redundancy*

It's about 1/3 of the diameter of 550 (type 3) paracord. Has no internal strands. If I put shrinkwrap over the 26 AWG wire it would be too big to fit in.   This image will give you an idea of the size 

Does any have any tips or tricks to feeding 26 awg wire through Micro Paracord (Type 1). It's taking me like an hour to do a foot at a time.