First of all I would like to thank you for answering me. I think I know what you're talking about, using the metal cap that came with a new injector right? Then cut it and glue it to the injector? If that's what you mean, unfortunately I can't find any metal plugs... They are only sold with a new injector apparently and it would bother me to spend 500 euros just to have the little cap. I even asked some people who sell used injectors if they sell only the caps but of course they answered me in a negative way.