This is just a "heads-up" to anyone who uses six-speed freewheels: I took off my Shimano TZ20 yesterday to do some maintenance, and I noticed that all my drive-side spokes had been abraded at the point where they enter the hub. I looked on the back of this $10.00 freewheel, and saw that there were rivets protruding from the largest sprocket (cheap manufacturing process). The rivets all showed noticeable wear on their forward side.
I rode with this cheap, Chinese freewheel for one season, and it appears I just got lucky by not popping a spoke.
This is my own fault. I knew it was crap when I saw made in china written on it.

Interloc (way to go), Suntour (NOS) and Sachs (If you can find them) seem to be the standard to-this-day.