I tried knitting with the size 9 on the smallest cable which I think equals 17" and found I could not knit with the small cable. Is it just me or do other people have this problem? If other people have this problem I’m wondering why they even put a cable that small in the kit? :shrug:
Measure from needle tip to needle tip to get measurements. It’s not the smallest cable that gives you 17 in. Use that one to extend cable length when needed. 
Or use that small one as a stitch holder! 
The needle tips themselves are about 3.5 in. The smallest cable is 5 inches and I only use that one for extension or as a stitch holder as previously mentioned. The next largest cable is 9 inches and makes a 17 in. circ needle. I use that all the time for hats since I have never made a hat that is smaller than 17 in. it works great.