Industrial pipe expansion joints.
https://diqn32j8nouaz.cloudfront.net...ipe_elbows.jpg
Previously:
https://www.homemadetools.net/forum/...409#post158387
https://www.homemadetools.net/forum/...505#post135848
https://www.homemadetools.net/forum/...512#post147198
https://www.homemadetools.net/forum/...697#post147846
https://www.homemadetools.net/forum/...719#post159599
