I got a Trem-Nut nut, pre-cut, at 1/8 thick.
It was pretty darn close right outta the package. I needed to take about .025 off the bottom of it, and trim/smooth the sides to fit, but it was no biggie. Once installed, I worked on individual slots to get the action perfect. No complaints whatsoever. As has been said though, there's really nothing inherently wrong with the stock plastic one. The only reason I changed mine is 'cause I totally modded my SX and basically wanted to swap out everything. That and the fact that I wanted a black nut to go with the black blocked and bound neck
