Fuel Line O-ring size?

I have an 88 XJ and I replaced the injectors today. Unfortuneatly when I was putting on the fuel rail and connecting the lines I realized the o-ring or washer in the back fuel line was cracked and broken.

What size is that and where could I find a replacement?

Thanks for the help.

I bought a variety pack from auto zone and just matched em up best I could.

I think the supply is 3/8 and the return is 5/16.