With the Kettlestack QuickChange feature the difference between a 72lb and a 60lb Kettlestack is about 10 seconds:

Yes, once you get used to the allen key tool, it takes about 10 seconds to "drop" the left wing- a bit more to replace it. "Quick Change" is an exclusive feature of the Kettlestack Adjustable Kettlebell handle. Your hand will naturally find the new balance point on the curved handle and a majority of the Kettlestack's shape remains intact. You can vary the "drop weight" up to about 1/3 of the total weight to suit your own personal needs.Just keep the tapered side closest to your thumb for comfortable shoulder cleans and get back to cranking out the reps.

The Kettlestack quickchange feature fits perfectly with minimal adjustment, whole-body kettlebell motions and a pair of adjustable kettlebells (well, even one) form the basis for a great compact (or budget!) home or traveling gym

If you go to our Assembly Instruction (+cartoon) page you'll see this bolt diagram

which shows both the one and two bolt setups; The two bolt setups "open up" these quick change possibilities.

BTW, the key to the one/two bolt choice is the fact that there's a flange welded to one side of the hexaxle.