Metric hex nylon insert lock nuts, Stainless steel 18-8 (A-2), 16mm x 2.0mm
Nut size (A.K.A. diameter) is the size bolt that the nut is used with. The same is true of the thread pitch. Thus a 6mm x 1.0 nut fits a 6mm x 1.0 bolt.
Note: Stainless lock nuts may require extra care during installation to avoid galling (seizing up). More info.