Copy Custom Number Format to other spreadsheets

I have a custom number formant which I need to apply to a number of spreadsheets.

Is there a easy way I can apply this to all spreadsheets; at the moment I have to go into each one and retype the entry in the custom format box.

Nearly every spreadsheet we use has a certain number format* - at the moment I copy and paste from one spread sheet to another - I'd like it so that it's automatically available in any spreadsheet that I open