Centre contact is split to improve electrical contact with plug, but in some cases the slot is closed at the tip, completely defeating the purpose. It can be spread open a bit using a very small screwdriver. The pin looks like it is cast, rather than machined.
The nuts are cast, not machined, and of poor quality. There is molding flash on the faces at the inside. Fortunately, the threads on the body are machined, so the nuts do fit without being grossly loose (just somewhat loose).
Overall, neither very good nor very bad. Certainly could be better.