Zoo Med Mag-Clip Magnetic Suction Cup

I’m using these in place of suction cups that have lost all flexibility. The magnet is strong enough to hold whatever a suction cup will hold - mostly filter tubes etc. They work just fine on my 120 gallon tank holding the filter spray bar in place. I have large fish and they have yet to move that magnet.

The magnet isn't very strong. If you have thin glass it would be ok but on my 90 gallon it barely holds

I use them as magnetic probe holders.
The magnet is to strong for the cheap float switches to be close to them.

for the Price i wasn't expecting much, but they do the job.
I am using them now as holders for a DIY protein skimmer and they hold it on the glass fairly well.