These drying tubes make it easy to see color changes when using indicating desiccants. Unbreakable polyethylene straight tubes, 16mm I.D. x 19mm O.D. (5/8"x 3/4"). Each tube is supplied with two polypropylene fittings that accept 6.4 to 9.5mm (1/4" to 3/8") I.D. tubing. Drying agent not included.