When you're making your own SPEAKON speaker cables, generally, bigger is better (when it comes to the amount of copper in your cables). More copper = less resistance, which allows your speakers to reproduce sound as intended by the amplifier.
However, if your cables need to be short (perhaps for Bass head to cab leads), or not needing to carry boatloads of juice, then the requirements for cable OD the size of Hulk Hogan's biceps are not essential.
This brings us to NLRR, designed for use with small cable O.D when working with the industry standard SPEAKON connector - NL4FX.
NL4FX is best suited for cable O.D of 7 to 14mm, so if you're going with something a little less chunky, pop an NLRR (strain relief reduction ring) into the mix, and you'll still ensure excellent cable strain relief - taking pressure away from the actual contact assembly.
NLRR works effectively for loudspeaker cables with an O.D. of 5 to 8mm.
Check out the range of genuine Neutrik NL4FX SPEAKON products available at Factory Sound