what is extra o-ring with tap connector for?

[crobar]

I've bought a couple of hep2o tap connector fittings, 1/2 inch female to 15 mm push fit.

All very well, but in the packet there are two things, the fitting and an o-ring. It seems like there's already an oring in the fitting, so my question is, what is the other one for?

I added a pic of fitting and spare oring

 

[Madrab]

If there's already a seal in the fitting then they've been nice and given you a spare

 

[crobar]

If there's already a seal in the fitting then they've been nice and given you a spare

Thanks, I thought maybe it was jyst a spare but thought I better check

 

[Phill Peck]

If there's already a seal in the fitting then they've been nice and given you a spare

Inspires confidence in the original one....