Go to EDIT > PRESETS > PRESET MANAGER
Choose Brushes under 'Preset Type'.
Choose the custom brush you wish to save to an .abr file.
Select 'Save Set'.
Choose the file location where you would like to save the .abr file.
Click save.
Thanks. I did it. I did it once before, I just forgot (happens a lot).
I had to remake it tonight 'cause the original got lost. It was a jack o lantern