Boot sub Definition


Boot sub:

A device made up in the drill stem above the mill to collect bits of junk ground away during a milling operation.

During milling, drilling mud under high pressure forces bits of junk up the narrow space between the boot sub and the hole wall.

When the junk reaches the wider annulus above the boot sub and pressure drops slightly, the junk falls into the boot sub.

A boot sub also can be run above the bit during routine drilling to collect small pieces of junk that may damage the bit or interfere with its operation.