I've used 2 or 3 of these: http://www.ebay.com/itm/291122353744...%3AMEBIDX%3AIT
Looks like the same as the Amazon ones. My only issue was putting the magnet somewhere. Those little magnets are hard to make stick. On my metal lathe it just found a place and stayed.....I left it alone and to this day it still works. On my drill press, for some reason, it got real touchy about the magnet placement, but now works fine. You can't beat the price.