Mikey3011:
I was thinking about a 3A 1000V Unidirectional Silicon Diode or 6A alternative?
What is a "Unidirectional Silicon Diode" the words Unidirectional are exactly what diodes are not.
EDIT :- Sorry brain fart.
That voltage is way over the top. The reverse rating only needs to be able to cope with the supply voltage so 50V would be fine. When the motor is generating hundreds of volts back EMF the diode is conducting and so the reverse voltage rating is not an issue.
The current rating of 3A sounds light, you should have a current rating of the same order of magnitude as the normal running current.