Deep Hole Drilling Glossary of Terms

Deep hole drilling is a metalworking process performed by precision machine tools.  Many standard terms used in manufacturing technology apply, however there are some specialized terms and acronyms unique to deep hole drilling that may not be immediately understood without some explanation.  Below is a brief Glossary of Terms that are useful when working with deep hole drilling applications.

Bottle Boring Tool

A tool which is used to machine an internal profile within the length of a bore, by using a cutting insert which is extended and retracted with CNC capabilities on a BTA equipped deep hole drilling machine.

Bottom Forming Tool

A tool used to finish a profile into the base of a blind hole, often to forms such as radii, steps, and flat bottoms, and used on a BTA equipped deep hole drilling machine.

BOZA (BOhröl-Zuführ-Apparat)

Term for pressure head in the German Language (translated as: Drilloil-Delivery-apparatus)

BTA (Boring and Trepanning Association)

Term referring to deep hole drilling tools where cutting fluid is introduced around the outside of the drilling tool, and chips are exhausted through the center of the tool.  These tools are normally larger than gundrilling tools.   More about BTA drilling

Counter Boring Tool

A tool that is used to enlarge existing holes by removing stock for a larger inside diameter, which is used on a BTA equipped deep hole drilling machine.


An operating mode of drilling for cylindrical parts, where the workpiece rotates in the opposite direction of a tool, which is also rotating, in order to improve concentricity of the hole.

Deep Hole Drilling (DHD)

A broad term used for drilling holes with a high depth-to-diameter (D:d) ratio, typically 10:1 or greater. Gundrilling and BTA drilling are types of deep hole drilling.   More about deep hole drilling

Deep Hole Machining (DHM)

An extension of deep hole drilling that creates machined features inside deep holes. Counter-boring, bottom forming, and bottle boring are common methods of deep hole machining.

Ejector Drilling

A term referring to the Double Tube System, previously used by the tooling manufacturer Sandvik.

ELB (Einlippenbohrer)

Term for gundrill in the German Language (translated as: single lip drill)


A term of art for the deep hole drilling tool that uses a single effective cutting edge, gundrills produce deep holes with high precision and productivity. Gundrills were originally developed for firearm manufacturing, but are commonly used in all industries. These tools are typically smaller than BTA tools.   More on gundrilling

Pressure Head

A component mounted to a BTA machine to introduce cutting fluid to the drilling process, and precisely locate the drill bushing to the drilled hole entrance, while providing a seal around the drill tube. Rotating pressure heads act as a tailstock to support a cylindrical workpiece, and have precision bearings and seals that contain the pressurized cutting fluid.

Pull Boring Tool

A tool that is used to enlarge existing holes with exceptional straightness, by being pulled back through the starting hole on a tensioned bar. Pull boring is a form of counter boring.


A device mounted to the rear of a gundrilling spindle, used to introduce cutting fluid to a rotating tool from non-rotating fluid plumbing.

Single Tube System (STS)

An alternate term for the BTA system, previously used by tooling manufacturer Sandvik.

Skiving and Roller Burnishing Tool

A tool that performs two options in one pass – stock removal skiving, and cold working roller burnishing – to finish the inside diameter of a tube, typically used in hydraulic cylinder applications.

Trepanning Tool

A tool that is used to drill a deep hole into solid material, by cutting a larger diameter and leaving a solid core in the middle, on machines equipped for the BTA process.