Glass Material and Spherical Shape Optical BK7 K9 glass balls lens Buyer and Importer

I am interested in buying 1,000 pieces of 4mm diameter clear Optical BK7 K9 glass round balls (spheres) or clear Sapphire round balls (spheres).What is the durability (how hard is it to break)?What's the surface quality?Please send me you best pricing.Thank you. Seans the durability (how hard is it to break)?What's the surface quality?Please send me you best pricing.Thank you. Sean Show More