Bel-art f19961-0000 polyethylene 6″ drying tubes with polypropylene tube fittings, 12/pk drying tubes with tube fittings can be filled with desiccant of your choice. Each unbreakable polyethylene straight tubes, 16mm i.d. X 19mm o.d.(5/8″ x 3/4″), is supplied with two polypropylene fittings with serrated tapered end that accept 6.4 to 9.5mm (1/4 to 3/8″) i.d. Tubing. drying agent not included. note: sold in inner package quantity includes 12 drying tubes, priced per each pack.