Is it a plastic or a metal geared servo?
For the metal geared servos use anything that fits airtronics.
If you have a plastic geared servo though the airtronics will be too loose and probably strip. You can squeeze a futaba horn on to the plastic geared servos but it is a very tight fit. It won't fit on to the metal geared version.
The plastic ouput splines can also be a loose fit in a number of ko servo horns as well. - This isnt just on one servo I've got either. It has happened on all three of my plastic geared ko servos.
Note: I've never actually used kimborough servo horns but they should be the same as most other brands.