I have been using Perma-Grit Tools for years now and looking back at the composite building process, do not know how I lived without these... These seem not ever to wear out (I do take care of them) and give me a solution for problem sanding areas and requirements that I could never get the professional results these allow me to achieve. I started out with one block type sander, was wowed, then bought another and another. Then I tried the files and basically threw my other files in the garbage (ok, just to the back/bottom of my tool box but you get the point). PS: I mainly bought these for composite sanding but now they are my go to tools for wood, fiberglass, plastic and soft metals.