These kits include the new, much improved sealing arrangement incorporating a shouldered cylinder and square o-ring arrangement.  These kits are not for later SZ throwaway spheres.
Rebuilding spheres requires special tools which are available from BTW but we are also happy to do it for you.  Sphere exchange starts at $300 ea. which includes the price of the kit.  Turnaround is usually less than a week.
 
I created a forum post describing the sphere rebuilding process:
http://au.rrforums.net/forum/messages/17001/34377.html?1546892840