In spite of a few inaccuracies on definition of impedance above, what I think the gentlman who wants a 60 ohm actuator core means is that he uses a length of magnet wire that literally measures out as 60 ohms impedance (that is DC impedance which is ohms as measured with an ohm meter). You need to know the gage of wire he is using and then look up the ohms/foot of that gage and that type of wire in table to see how many feet of wire he is winding into the actuator. The radio amateaurs manual has that information as do many engineering text books. For those questioning definitions, ohm is impedance always but impedance can be more than just the ohmic value, i.e. capacitive and inductive reactance to ac signals which add to the dc component usually stated as "ohms" and effects only the ac currents.