carbide end mills

[knifer-one]

i have been considering some carbide end mills but it seems that a lot of them don't have flats for holders. Are these made just for collets?
will my end mill holders work with them?

 

[Tony Wells]

You see them in collets almost exclusively. I have ground flats for standard holders, but my feeling is that you lose concentricity with that type of holder. Carbide needs to run true. If you're pushing it hard, flats can keep it from walking out of the holder.