Thanks to input from fellow etsy jewelry makers I have found a better magnet clasp! It looks the same as the ones I was using, actually a hair smaller, but boy are they stronger!! The brand is Mag-Lok. The tip I got was to be sure that the clasp has Mag-Lok imprinted on it.
After researching prices I opted for a local internet bead retailer - Artbeads - in Gig Harbor. I ordered a few 6mm and 8mm to see if I liked them. The 8mm are too large for my tastes - and I could barely get them apart! Today I placed an order for more of the 6mm size in silver and gold plate. They are plain, but most of fancy ones I have seen are just not strong enough. Sometimes function is more important than looks! For my glass garden bracelets I will only use Mag-Lok magnets from now on.
If you have one of my glass garden bracelets and have been unhappy with the strength of the magnet please contact me and I will replace them with these new stronger magnets free of charge.