From the maker of the SuperDuo beads,  the GEMDUO beads are very similar to the Diamonduo, both beads are diamond-shaped with a flat bottom and two parallel holes. The big difference between them is the top. DiamonDuos have four faces that come together to a center point, and GemDuos have a gently beveled top with slightly raised center ridge.
 
The two holes are 4mm apart (center to center)
Accommodate wire or thread up to 20 gauge (0.812mm) thick
Measurements: 8mm long and 5mm wide
Quantity: 10 gram tube or bag 
Color: Jet Hematite (GD8523980-14400)