F-Connection Diamond Core Drill Bit Dimensions & Drilling Depth

Gunther F-connection diamond core drill bits are designed specifically for Gunther precision drilling systems, including the Multidrill Water Swivel, Hobby Drill Press, and TBH Pro 2 and TBH Pro 3 bench drilling machines.

The diagram below illustrates the key dimensional terms used to specify these drill bits and explains how each dimension relates to drilling depth, tool life, and system compatibility. A complete table of dimensions is locate further down this page. 

*Reference diagram showing dimensional terms used throughout the specifications below.

Definitions:

Ejector Needle - A precision needle that runs through the hollow core of the drill bit.
It assists with material ejection, cooling, and chip removal during drilling.

F-Connection - The threaded connection interface used to mount the drill bit into Gunther F-connection drilling systems.

This interface provides precise alignment between the spindle, drill bit, and ejector needle.

L1 — Support Length (Non-Cutting Length) - The solid, non-diamond section of the drill bit shaft behind the cutting area.

L1 represents the repeatable drilling depth that can be achieved over the full usable life of the tool, because this length does not change as the bit wears.

If your project requires a specific, repeatable drilling depth, use L1 as the governing dimension when selecting a drill bit. This ensures the required depth can be achieved consistently over the full usable life of the tool.

L2 — Cutting Length (Diamond Length) - The length of diamond-impregnated material behind the cutting edge. In a diamond core drill bit, cutting occurs at the rim, not along the length. 

L2 provides diamond wear reserve and determines tool life, not drilling depth. As the bit is used, this section is gradually consumed, shortening the overall length of the drill bit.

Outer Diameter (OD) - The outside diameter of the drill bit, shown in both metric and imperial units. OD defines the finished hole size produced by the tool.

Inner Diameter (ID) - The inside diameter of the hollow core. ID affects flushing performance and determines compatibility with the ejector needle. ID also defines the diameter of the core removed during drilling.

Grit (FEPA / US Mesh) - The diamond grit size used in the cutting rim. Lower numbers indicate coarser diamonds; higher numbers indicate finer diamonds.  Both FEPA (European) and approximate US mesh equivalents are shown for reference.

How to Read the Table

• Diamond core drill bits remove material at the rim. Material removal occurs at the cutting edge, not along the body of the bit.
• Cutting length (L2) does not define drilling depth. L2 represents the length of diamond-impregnated material and determines diamond wear reserve and tool life, not how deep the tool can drill.
• L1 + L2 equals the total length of a new drill bit at manufacture. As the drill bit is used, the diamond-impregnated cutting section (L2) is gradually consumed, shortening the overall length of the tool over time.
• For applications requiring a specific, repeatable drilling depth throughout the life of the tool, L1 is the governing dimension. Because L1 does not change as the bit wears, it is the correct reference for consistent depth control.
• In Gunther alignment systems, drilling is often performed from both sides of the workpiece. When drilling from both sides and meeting in the middle, total achievable hole depth can exceed the length of the drill bit itself. As a general guideline, up to approximately 2 × L1 can be achieved under proper setup and alignment.

Legend:

• Gray rows → Standard Sizes (In Stock)
• White rows → Custom Sizes (Made-to-Order)