For extension rod, there are two shapes, one is round type, and another one is hexagonal type. All extension rods are threaded and made by hollow drill steels.
This hollow hole are usually named flushing hole, used for transmitting water or air during drilling. Two ends threads can be used for connecting couplings, shanks, couplings or bits. Typically two ends of extension rods are male, while sometime one end is male and another one is female, then we call it M/F rod. We need couplings to connect extension rods , while for M/F rods, because one end is female, so couplings are not necessary.
Extension rod size:
R32-Round32-R32 | length 3 4 6 8 10 12 feet |
T38 (R38)–Round39-T38 (R38) | length 4 6 10 12 feet |
T45-Round46-T45 | length 10 12 14 20 feet |
T51 -Round52-T51 | length 12 14 20 feet |
MF rod/speed rod size:
MF-rod R32-Round32-R32 | length 3 4 5 6 10 12 14 feet |
MF Rod T38-Round39-T38 | length 4 5 6 10 12 14 feet |
MF Rod T45-Round46-T45 | length 5 6 10 12 14 20 feet |
MF Rod T51-Round52-T51 | length 6 12 14 20 feet |
MF Rod ST58-Round60-ST58 | length 12 14 20 feet |