Cheap threading
"I took the shade, fixture, and my 1930s gooseneck lamp base to a professional to have it rewired/restored to working condition. The owner said the threading on the shade was cheaply done, and we had difficulty attaching it to the fixture. After some struggle, I got it to fit, but just barely. The owner made me do it because he wanted me to be responsible if it broke. I had a similar brass shade whose threading broke off in pointy shards (same manufacturer?). Hopefully, if the lamp is put somewhere where it won't be disturbed, I'll be okay with my purchase. The "library green" color is perfect, though."