3/4" (19.05mm) OD x 3/8" (9.52mm) ID x 1/4" (6.35mm) thick, magnetized through the thickness.  This is a maximum strength magnet for high temperature applications. The maximum working temperature of 300C makes this a very special magnet.  These are not as strong as their neodymium counterparts and they are more expensive, but if you need a strong magnet at high temperatures, this is the one.  These are nickel plated to minimize chipping.

Price per piece.