For glass up to 1/2" thick. Mega Mag glass cleaners are completely sealed and corrosion protected and are suitable for use in fresh and saltwater aquariums. The large cleaning surface makes for quick and easy use, while the construction of the body with its slender extended edges facilitates cleaning the most difficult areas. The cleaning pads of the inner magnet and the felt pads of the outer magnet can easily be replaced. A cord can be fixed to the inner magnet enabling it to be easily retrieved from the aquarium. Mega Mag glass cleaners contain extremely strong neodym magnets and have to be handled with care.