Rubies in armor or helms provide useful hit point bonuses, and are commonly socketed in merc equipment.
Diablo III Rubies
This gem type returns in Diablo III, but with very different bonuses.
Diablo II: Lord of Destruction
These are the bonuses provided by a Ruby in D2X:
| Quality | Weapon | Helm or Armor | Shield | Clvl Req | |
|---|---|---|---|---|---|
| Chipped |  | +3-4 Fire Damage | +10 to Maximum Life | +12% fire resistance | 1 |
| Flawed |  | +5-8 to Fire Damage | +17 to Maximum Life | +16% to Fire Resistance | 5 |
| Normal |  | +8-12 to Fire Damage | +24 to Maximum Life | +22% fire resistance | 12 |
| Flawless |  | +10-16 to Fire Damage | +31 to Maximum Life | +28% fire resistance | 15 |
| Perfect |  | +15-20 Fire Damage | +38 to Maximum Life | +40% fire resistance | 18 |
D2C Ruby Stats
Rubies have slightly different stats in D2 Classic.
Ruby
| Quality | Weapon | Helm or Armor | Shield | Sell Price | Clvl Req | |
|---|---|---|---|---|---|---|
| Chipped | | +3 fire damage | +6-8 to maximum life | +11% fire resistance | 125 | 1 |
| Flawed | | +4 to fire damage | +10 to maximum life | +15% to Fire Resistance | 375 | 5 |
| Normal | | +4 to fire damage | +14 to maximum life | +19% fire resistance | 1250 | 12 |
| Flawless | | +5 to fire damage | +19 to maximum life | +24% fire resistance | 3750 | 15 |
| Perfect | | +6-7, 6-8, or 6-9 fire damage | +24 to maximum life | +29% fire resistance | 7500 | 18 |