Wheel bolt/nut covers

[Archangel]

Hi fellow enthusiasts. I'm sure the answer is somewhere here, but I'm just too lazy too look. What is the correct size for the plastic wheel nut covers.17 mm or 19 mm. I'm missing a few and want to replace them. Also any difference in quality between oem and standard you can buy on Amazon?
Thank you for any help.

 

[EddieJ]

17mm, can be some poor one on amazon/ebay but with really only the domed cap showing, who is ever going to know.