Telescope T2-Extension Tube Kit for Cameras and Eyepieces - Length 7mm 10mm 20mm 30mm - M42x0.75 on Both Sides

I ordered a set of tubes and quickly noticed that the 20mm tube female threads would SLIP ON AND OFF the male threads of the 30mm and 7mm tubes (but not the 10mm tube). The 7mm also slipped on & off the 10mm tube. So I did a return through Amazon and got another set. Same problem with the 20mm tube.So yeah, I'm not expect the best quality for these cheap tubes, but I do expect them to know how to use a lathe properly to cut a proper M42/0.75 thread.Obviously, I'm not going to attach my $1000 camera to these tubes.Also, these seem to be anodized rather than say powder coated. I don't really care which, but the inside of the tubes should be matte not glossy, so even the tubes that are cut properly aren't that great.