Part of my problem before was that I had not yet put the rubber pads on the magnet, which allowed it to slide rather easily. Doing so helped, and kept them in place, but, there's nowhere near the holding force of the .75" rated magmounts for the Streams, as you can easily pull it off the glass accidentally when trying to adjust the direction of the pump's flow. It doesn't move at all on the thinner 1/4" glass of my 40G tank, however.