If you can, take a short piece of pipe with you when you buy them. I've got some that are around 30 years old that I think I got from Sears and they work great. I bought some more later, probably Chinese, and I have a hell of a time sliding them up and down the pipe. Sometimes I have to hammer them to move them. It might be due to a metric to Imperial conversion mismatch. Make sure they work smoothly or you'll be ticked off every time you go to use them.
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