Rinzl Plastic Unbreakable Cover Slip, 22mm Length x 22mm Width x 0.007" Thick, Clear (Pack of 1000) An excellent addition to your science classroom Due to the sealed metal electrodes on the end of the tube, spectrum tubes light up when placed in the power supply A great supplement to your matter lessons Economically priced to fit your budget Easy to handle, break-resistant shell makes it perfect for student use