That's an interesting looking lump - what is it?
If I'd known you were going to ask me that. I'd have taken a lot
more pics, back in 2003.
They were called segments...... A fat, wobbly profile "flag", on a stumpy post.
(The post hasn't been machined yet, in this shot)........
The post, goes in the hole bored in the bottom of the recess.......
Allowing it to swing outward, under drilling forces. So, producing a larger hole, than the body. Allowing a steel casing to follow down the hole.
At the bottom of the hole, a reverse turn rotates the segments back into their recesses. Allowing the drill string, and body to be extracted, leaving the casing in place.
As explained here..... http://www.americawestdrillingsupply.com/bulroc/CDS745.asp
Watching the film, shown some weeks after the event. I believe this was the equipment used, to open the hole to rescue the Chilean miners, in 2010.