This holder will keep all your dosing tubes secured and out of the way. - 1/4" bulkheads for firmly holding standard 1/4" OD tubing - Strong Neodymium magnets combined with a grippy oring hold securely in place on aquarium thicknesses up to 3/4" - Magnets are completely encased in cell cast acrylic and will never get water in them. No worries about rusting magnets causing water quality issues.