Designed to use Neodymium Magnets 2" x 1" x 3/4" works great for 3/8" glass also up to about 1/2" use the soft side of Velcro on the outside glass part and the hook part on the inside to clean the algae Print 80% fill 3 shells ABS Then an ABS slurry to glue the 2 parts together doesn't float, but works way better then what you can get at the store. Be careful as the magnetic are extremely powerful and you could loose a finger. http://www.ebay.com/sch/i.html?_from=R40&_trksid=p2050601.m570.l1313.TR0.TRC0.H0.TRS0&_nkw=Neodymium+Magnets+2%22+x+1%22+x+3%2F4%22+&_sacat=0