501 W5W Capless wedge bulbs 12V 5watt is the correct description.
Best of luck finding the right one though, I have tried 3 sets so far to try and match the Philips Extreme H7 main bulbs I have fitted and have not found the correct hue yet. they all seem to be police beacon blue!!
Amazon have a selection and seem to be cheap, I have seen them recommended by another forum, autobulbsdirect.co.uk is another source of info but seem expensive.