I'm looking for rare earth magnets, or any similarly strong magnets, that will fit in the bottom of 25mm slotted bases. I need the same for the 20mm slotted bases as well. What size do I need and where can I find them online in the US? I'm completely new to magnetizing.
There's a bunch of websites that sell them. I forget which one I used since its been so long. If you buy them direct you get a hundred magnets for only a few bucks so just google rare earth magnets and browse around. The only thing i'd look out for is shipping. Don't buy them second hand, like from a game store, because they'll gouge you.
eBay is definitely your friend. All kinds of different shapes, sizes, and prices, but they're all pretty cheap. If I recall, I think I got about 50 for $5.
https://www.amazingmagnets.com 12 bucks for 100 suitable magnets. i havent bought any, but the site seems good enough to me.
I use ZD1 magnets from K&J Magnetics (http://www.kjmagnetics.com). They are 6mm round by 1.5 mm thick which fits easily under Saurus or Skink bases. They hold securely, even upside-down, but the models are still easy to remove. I just looked at the web site and it looks like the price has gone up since I ordered, but it is still pretty cheap ($16 US for a pack of 100) and there is a sale for the rest of the month.
to magnetize bases i would use cheaper "normal" magnets, since there isnt too much stress on it. to magnetize models, like a stegadon howdah, i would use the rare earth stuff.
For small things like arms and feet, you want the smallest magnets you can find. I think either 1/8 or 1/16 of an inch rings a bell for mine? They still have pretty reasonable strength, plenty for holding limbs and such in place. For other stuff, the best way is to get a ruler with mm on it and measure your application. Ensure there is room around it to drill a hole if you need to, but go for as big as you think you can get away with because the bigger they are the stronger the bond.