1. Before and after centralizer is adopted which can centralize and reducing the friction pretty well. The reasonable design makes the sand returning effect perfect.

2. Security protection device is added which reduces the drill drop accidents effectively.

3. Different specifications of reamers are applied on different stratum and borehole size.

4. The cones are metal sealed whose work life is much longer; Wearproof ability of metacarpal  is much more stronger;

5. The tail of reamer is tapered which is convenient to pull back.