10x5x2.5mm (approx 7/16" x .2" x .1") neodymium block magnet.  Only slightly shorter than the 12.5x5x2.5mm.

Magnets are great to use in your polymer clay projects.  Please note: Magnets lose their strength when they are heated so don't bake them.

Developed in the 1970s and '80s, rare-earth magnets are the strongest type of permanent magnets made, producing significantly stronger magnetic fields than other types such as ferrite or alnico magnets. There are two types: neodymium magnets and samarium-cobalt magnets.

• All magnets may chip and shatter, but if used correctly can last a lifetime.
• Keep away from pacemakers.
• Not for children, parental supervision required.
• Handle magnets with care.  You can easily pinch your fingers.  Slide them apart instead of pulling them apart.
• Heating magnets can weaken them.