Just finished this today , my take on the frag rack. I am using nickel plated DXO2's on the inside and found out that using two of these would not work, so using DXO6's on the outside.
The PVC caps are 3/4" and I cut a "spacer" of 3/4" PVC to fill the inside of the cap and allow the 1/8" thick DXO2 to fit or the DXO6 3/8" to fit and close off the opening with a piece of 1/8" acrylic. I used #16.
On the next rack, I'll just use the DXO6's as there are stronger, thicker but cost more and are on sale 20% off - don't know how
long
On the outside shot, the left cap has not been trimmed off yet, that's why the rectangular "foot". Next one will be little larger and wider and will need 3 (6) magnets instead of 2 (4)
NOT so the guy at K&J said that the DXO6's would work better. Since I already enclosed 2 of the DXO2's, I thought that if I used the 6 on the outside that might work - it does but I only have 5 of the 6's and 10 of the 2's. Oh well
I wouldn't worry about the force used to take the magnet off, if you enclose it, like I did you just move the magnet away (slide it off) and it's the same way to attach it, slide it on. This way you don't have to worry about cracking the glass if it grabs it out of you hand, and it will. 
