Rock formation

Bit type

Bit size

Drilling weight

Rotary speed

mm

inch

kN/mm

r/min

Very soft

Soft Marl, Clays, Sands, Salts etc.

1

187.3~346.1

7 3/8~13 5/8

441~735

120~50

soft

Clays, Soft Shale, Marl, Sands, Salts etc.

2

95.2~174.6

3 3/4-6 7/8

245-490

100-50

187.3~346.1

7 3/8-13 5/8

490-784

90-40

Medium soft

Shale, Marl, Sandstone, Soft Limestone etc.

3

95.2~174.6

3 3/4-6 7/8

245-490

80-40

187.3~311.1

7 3/8- 12 1/4

490-784

80-40

medium

Hard Shale, Limestone, Medium/Hard Sandstone etc.

4

95.2~174.6

3 3/4-6 7/8

294-539

80-60

187.3~241.3

7 3/8-9 1/2

539-833

60-40

medium hard

Hard Dolomite, Limestone, Hard Sandy, Rock etc.

5

95.2~174.6

3 3/4-6 7/8

294-539

80-60

187.3~241.3

7 3/8-9 1/2

539-833

60-40

hard

Sandy, Shale, Quartzite, Hard Dolomite, Hard Sandstone etc.

6

95.~-174.6

3 3/4-6 7/8

294-539

80-40

187.3-215.9

7 3/8-8 1/2

580-882

60-40

Very hard

Quartzite, Chert, Basalt Granites, Pyrites etc.

7

95.2-174.6

3 3/4-6 7/8

294-539

80-40