... sandstorm, salt, etc. Recommended Bit type: 437, Drilling weight: 0.35~0.90 KN/mm, Rotary speed, 240~60 r/m ... , soft limestone, etc. Recommended Bit type: 517, Drilling weight:0.35~1.05 KN/mm, Rotary speed, 220~60 r/m ... limestone, sandstone, etc. Recommended Bit type: 537, Drilling weight 0.35~1.05 KN/mm, Rotary speed, 200~40 r/m ...