... . YWD 50 and 70 is the best quality stones made in lab condition, the production quantity will be few, but ... engineering, mechanical processing etc. YWD 2290 consistent crystal color, regular shape, good trandparancy, high strength and great thermal stability, ... saws, frame-saw and geological broaches. YWD 2140 comparatively regular crystal shape, high mechanic strength, beolonging to middle grade, ...