These words "Gratdübel" and "Riffeldübel" don't seem to have direct translations into Slovenian. They refer to specific types of wooden dowels with certain features: "Gratdübel (utorjeni moznik)" likely means a dowel with a fluted or ridged design for better glue adhesion, while "Riffeldübel (rebrasti moznik)" refers to a dowel with a ribbed surface to hold more glue and create stronger joints. Since there isn't a straightforward translation, it's best to describe them by their characteristics when talking about them in Slovenian, perhaps using terms that highlight their grooved or ribbed nature.