pretty sure all the stuff from china uses 5140 steel... that's how they keep the price down (hehe). if the inserts are replaceable that's def a step in the right direction (In my friends case they weren't, but this was a while ago)... but at that point you start questioning the threads that hold that nut in. if that insert starts to wobble... your guitar will explode at high speeds! further the threads on the posts/studs, the threads on the screws holding the string blocks, etc. my exerpience w china is that they are anything but precision afa threads are concerned. their metal in general isn't great ime, but I have had some positive experiences too so... ymmv.