These "flexible collars" go in next and provide the weight on the bit. The drill string is kept in tension while drilling! The stainless steel collar on the left is required when the direction is checked with a compass (every 4 rods when I was there) and costs about 10.000 dollar... The divice that is lowered into the drillstring (called "camera") measures magnetic north and inclination. By plotting these as the hole progresses you have an accurate idea where the bit is.