my friend in El Paso has these in her setup kit. she uses to magnet tarps to her van and other things. one came home with me, so I can make my own. I have the circle magnet, and bolt/nuts. But I cannot find the steel "cup" that the magnet is in at my local hardware stores. Question: what is JUST the silver cup thing, and can I get them without the magnet? here is what I found online today: https://www.grainger.com/product/49M039 http://www.choumag.com/CeramicCupAssembies.html Next questions: how do I determine pull strength without equipment? what would be strong enough to magnet tarps to the steel pole/roof cabanas at my fave ACE parks, that will withstand the 35mph Texas 'breeze'? what would be toooooo strong to pull off by hand? #75? Thank you in advance. I know someone here will have the answer!