Injector O-Ring's size?? 3.1L engine

Hi,
Anyone know the size of injector o-ring on 3100 engine??
After replaced the upper and lower intake gasket, the gas spills out from fuel rail when I start it.
I search on oreilly and autozone, the injector oring is ~$1 each. I remember Harbor freight tool sells oring set with 300 rings for under 10 bucks.
So I want to know if it is of socalled 'AS568' standard (in inch), or matric size?

Many thanks