I ordered 20mm square 3mm thick wooden bases from Litko. This is my standard base thickness that I use for all of my 28mm figures. I then ordered thin metal bases that corresponded to the Piquet infantry stand sizes: 30mm by 60mm. My plan was to put magnetic adhesive squares on the bottom of the individual bases so they would stick to the metal Piquet stands when players moved them. This plan also left me other options in case I decided to try rulesets that had different basing requirements. Sounds great, right?
The problem was that the dang magnetic strips weren't strong enough. They would fix the figures to the stands, but if you tried to lift them at all, the magnet would release the metal base and the figures would fall off. I could just see myself moving my mounted retinue knights in for the kill and then dropping them all over the table, "Ha Ha!, (CRASH, BREAK, BEND)
I've also learned over time that figures you plan to use at a convention have to be very securely attached. Anything you imagine might be done to them, will be done to them. They will be dropped, stepped on, leaned on, dipped in ketchup, punted across the room, and pelted by dice, all by apologetic gamers who get a little carried away during that critical melee. Now maybe you understand my obsession with gloss coat varnish. Hmmm?
So, to solve my problem, I decided to use my old stand-by. Rare earth magnets. They sound very mysterious and magical, as if they're mined by elves from the center of the earth, but the little suckers are really powerful. I've used them before for my ACW artillerymen. I can actually hold one of my cannons upside down and the gunners will stay on the gun's base.
I don't order them from any gaming outlets. I use a company called Amazing Magnets. http://www.amazingmagnets.com They're in Irvine, CA behind the Orange Curtain and they offer a tremendous variety of magnets in different sizes and shapes for a reasonable price. I usually receive the magnets the day after I order them.
First, I drill a hole in the bases with a 1/4 inch drill bit. Watch the fingers! I use pliers.
Then I get the little magnet off the stack and crazy glue it in the hole. I sometimes have to tap it with a small hammer to make sure it sits flush with the bottom of the base.
I like the lighting in this picture. It looks like an evidence photo from the Unabomber's workshop.
Here's the end result. I hot-glued (is that a verb?) the figure on the top of the base and then covered it with dirt and static grass. Now this little guy will stay on a metal base until you give him a good tug.
I use at least 1/4 inch magnets because the smaller diameter magnets don't have enough magnetic attraction to do the job.