I don't usually include a pull cord with my light pulls as most people have an existing pull switch. However sometimes a you might need a spare cord.

These are 3mm nylon cords and each one will have the little plastic widget which attaches it to the majority of pull switches.

I choose 3mm cord as it fits snugly in the top hole of my pulls. a thinner cord will thread more easily but doesn't hang straight and may wear more quickly. I know this makes them a little tricker to thread so i put together a handy guide as to how I tackle them.