'Only 1 D20' : It will comes with only 1 dice(D20).
'Full Set of Dice' : It will comes with 7 pieces of dice(D4, D6, D8, D10, D%, D12, D20)
'11 pcs of dice' : 11 pieces of dice come with a full set of dice(7 pieces) and an extra d20 & 3 additional d6.
Gemstone dice are fragile, so I recommend that you can roll them on something with a soft surface, like a soft wool felt dice tray:
Size of each dice:
D4 = 16 mm
D6 = 16 mm
D8 = 16 mm
D10 = 16 mm
D% = 16 mm
D12 = 18 mm
D20 = 18 mm