Staton website says you need two spot welds on the freewheel, when you want to use it for the Nuvinci hub... Otherwise the site says it can "fall apart." Check 22 Tooth freewheel sprocket 1/2 x 1/8 with two spot welds
for that info.
Also, why do you need a freewheel in the rear, when you've got one already in the crank (shift kit)?
I have these lingering questions, when I need to have them answered.