On arrival I put it on my grinder for evaluation. Not good. One might think that with a 90 degree notch, parallel to the table, one could zero. no I had to grind/expand the screw holes in the base. In addition, the top surface of the fixed jaw was 0.002 inches higher at one end than the other. Sand the surfaces and oil everything (it came dry). When I reassembled it I noticed that the center pin in the base that the vise rotates around may actually have fallen off and didn't go into the hole in the vise. So I hammered it back into place and now it spins properly. This was probably the whole cause of the original problem, not the screw holes. In summary, it is now a fairly accurate instrument. straightens up parallel to the table at the ends of the jaw. Oddly enough, between 0.0005" and 0.0007" the center of the jaw is not flat (concave). I don't know why it is like this. But I think it's good enough for what I need it for. These are standard vices for a hobby shop like mine, but a real professional machinist might not be happy with them. On the plus side, it costs a lot less than the good ones.