Inner shell drilling first, the outter follow,Cutting ring with rock drilling bits rock；

Rock drilling bits perform stage breaking and drilling ;

Small barrel facilitates the coring operation; large barrel performs stage breaking;

Applicable layers: gravel，boulder, medium weathered rock；

Customizable Items
Cutting DIA. Custom : design various cutting diameter based on demand, like φ950、φ1050 etc.

Shell HIT. Custom : design as demand, prolong or shortten, increase of efficiency by drilling more.

Key Component Reinforce Custom : strengthen the key component to extend life cycle;

Kelly Box Custom : custom kelly box size based on the kelly bar, like 130*130, 150*150,200*200 etc;

Space between the shell Custom : custom the space between the double shell based on demand;