I can measure the shaft diametre with my micrometre if that will help.
I just did a quick Googke search for SkyTee II cables and found several forum threads on the topic and yes it will accept slo mo cables.
https://stargazerslounge.com/topic/1...cher-skytee-2/
http://s843.photobucket.com/user/sp3..._1182.jpg.html