Custom CTS potmeters have a much improved charteristics kcompared to the standard CTS potmeters:
By ordering the potmeters as 550K with a +/-9% tolerance the real value of the potmeter never drops under 500K. The potmeter has a much improved and more equal curve that makes the potmeters suitable for both volume and tone control. The brass shaft is more strong and less likely to break off like the standard zinq shaft.
The long bushing is suitable to mount the potmeter through a thick wooden top, like a Les Paul.
Why would you mount a good potmeter in your guitar when you also can get the best? ;-)