These frag racks will not disappoint! They will securely hold your frags in place, on aquariums up to 3/4" thick. - FDA grade silicone locking layer holds plugs securely. Nothing will knock them out. - Strong Neodymium magnets combined with a grippy oring hold the rack securely in place on aquarium thicknesses up to 3/4" - Magnets are completely encased in cell case acrylic and will never get water in them. No worries about rusting magnets causing water quality issues.