Kelly is the drive part of whole drill string, it transmit the torsional energy from the rotary table to the bit in the bottom of the hole. Boban precision-machined Kelly is a heavy square or hexagonal steel bar supported by the swivel through the rotary table and connected to the first joint of drill pipe in the drill string.

Straightness of the kelly is very crucial in the manufacturing process, thus straightness inspections are carried out before, during and after each machining operation. The flats are precision-milled to API specifications. All milling processes are performed on specially designed rigid Kelly mills to ensure tight tolerances and high quality drive sections. Each Boban Kelly is furnished with a pressed steel thread protectors.

It's the drive part of whole drill stem, it has two types, square kelly and hexagonal kelly and all of them are manufactured comfort to API Spec7-1 and SY/T6509-2000 criterion. Our Square and Hexagonal kelly are made from AISI 4145H modified alloy bars that are quenched and tempered full length. After such heat treatment, its brinell hardness can reach 285-341. Kelly's'end, drive cross-section and joint are all processed and tested comform to API criterion.