odd size bathroom sink water suplly line

[Scoobie]

Hi, I'm installing a new bathroom sink. The supply line I'm installing dosen't fit the 3/8 shut off. The supply line has a male screw fitting that screws into the faucet, the male screw end looks to be 1/4. The end of the supply line tube looked to be 3/8, but it doesn't fit the shut off. It's to big to be 1/4. Do you know what size this would be. When I try to fit it, the brass ring is ecxactly the size of the end of the tube ( will not go over the tube ). We bought it at Ikea, could this be metric?
Thanks,
Scott