Cast Alnico 5 is the most commonly used of all the cast Alnico magnets. This material is used extensively in rotating machinery, meters, instruments, sensing devices, and holding applications, to name a few.  Alnico is hard and brittle. cannot be Machined or drilled.  therefore be accomplished by ordinary methods. Holes are usually cored in at the foundry, and magnets are cast close to final size and then finish grinded to close tolerances.                                                                   http://www.sensmagnetics.com/