...Is this a universal adapter?.... or only works on the K&M....
You'll find, Bob, that all of the hardware mentioned in this topic is interoperable, (be it Frankenstand, Goliath, Hercules, K&M, On Stage or Ultimate) as nearly all modern speaker stands use a 35-36mm riser tube as their central speaker "elevator".
How heavy are the speakers that you are using with the K & M 213s?
The heaviest pair are my amazingly broad spectrum, long throw and weatherproof One Systems 112iM enclosures at 27.6kg (or 61lb) each, ...but I frequently need to ballast them against high wind loadings with a non-elevated load of up to a further 30kgs in the form of a pair of 15kg shot bags that I hang down low from the stands' central spreader mechanism ...and the K&M 213 is the only stand that I've found which will reliably do this, year in, year out.