A standard international ballpoint refill with a medium point and high-quality red ink.
Parker refills are all the same ones that come as standard in their pens, so if you have the old one to hand, you will have a great chance of matching the right one from the photo. If not, just use the type of pen to make the decision, as they will all be compatible.
All Parker refills use their well known quick drying 'Quink' ink, and come in a choice of two or more colours.
Any refills on this page not made by Parker, will still be compatible with their pens.