The models RED 1 and BLUE 1 use a 4 piece cantilever, of ‘’OTL’’ type (optimized transmission line), attached to a brass bushing. The coils are made of long grain, oxygen free copper. The diamond is of an elliptical shape special to GRADO. About 10% of the cartridges of this sub series will be stamped RED 1 following a serious inspection. The “bodies” are made of black plastic.