RockBit Tool Steel S2 Balls. S-2 Rock Bit Tool steel balls are suited to extreme conditions common to oil drilling, the material provide toughness, strength, shock and abrasion resistance. S-2 Rock Bit Toll steel balls have uniform hardness of 54 to 60 HRc. Diameter range: 3 mm – 25,4 mm: Grades: ISO 3290 G20-G100: