To those who don't know... (No connection to seller)... This particular ball head tripod mount is the best, light weight ballhead I know of.
I have tried several and this is the only one I would endorse. Someone who needs one, will get a good deal here.
What makes it special is its ability to lock firmly with moderate torque on the locking knob. Most other ballheads require more torque and are still less capable of holding still.