Cat. GG-20-Collagen: 20 mm diameter, # 1 thickness, 90 pieces of CE certified crystal clear German glass coverslips with rat tail type I collagen coating on both sides for cell culture, sealed 15 pieces per bag x 6 = 90 pieces, sterilized, ready to use. Alternative coverslips to consider: GG-18-collagen, GG-22-collagen.