BullseyeBore Core – Chuck Extensions

BullseyeBore Core Chuck Extensions are an optional accessory in the BullseyeBore Core ecosystem that fits between the drill chuck face and the back of BullseyeBore Core.


Chuck Extensions serve to move BullseyeBore Core forward along the drill bit and are typically utilized to move BullseyeBore Core’s projected Reference and Alignment Patterns closer together on the worksurface at the start of drilling, which can make drill alignment or misalignment easier to visualize. They can also be used to reduce the overall diameter of the Alignment Pattern (or Patterns) if they do not fit on the worksurface. 


The example below depicts a 5.75” drill bit and the resulting patterns at the start of drilling both with and without a Chuck Extension.

Core Green Extended with a 5.75” bit without a Chuck Extension

Core Green Extended with a 5.75” bit and a 1” Chuck Extension. Note how the Fixed Reference Pattern and Alignment Patterns are closer for easier alignment or misalignment interpretation.

The example below depicts a 7” drill bit and the resulting patterns at the start of drilling both with and without a Chuck Extension. 

Core Green Extended with a 7” bit without a Chuck Extension

New Paragraph

Core Green Extended with a 7” bit and a 1.5” Chuck Extension. Note how the Fixed Reference Pattern and Alignment Patterns are closer for easier alignment or misalignment interpretation.

Chuck Extensions are offered in size incremental lengths of 1.50”, 1.00”, and 0.50””.

BullseyeBore Core Chuck Extensions are especially helpful with longer drill bits (5”- 8”) when the entire length of the drill bit will not be used during the drilling operation. The area also helpful with longer specialty drill bits like Spade and Auger drill bits. This video depicts BullseyeBore Core with several different length Chuck Extensions and bits as well as the attachment process.

Some experimentation may be required to select the optimally sized Chuck Extension. This may be accomplished by visualizing the pattern on a worksurface with the target drill bit and different size Chuck Extensions installed. Chuck Extensions are offered in size incremental lengths of  0.50”,  1.00”,  and 1.50”.


Always read and follow the BullseyeBore Core Safety Guidelines before attempting to use BullseyeBore Core or any BullseyeBore Core accessories on a drill or in an actual drilling operation

Like BullseyeBore Core, Chuck Extensions connect magnetically to the drill chuck face. BullseyeBore Core then engages magnetically with the front of the Chuck Guide. The Chuck Guide also contains an extended ring that inserts into the BullseyeBore Core to prevent displacement between BullseyeBore Core and the Chuck Extension.

No, only a single BullseyeBore Chuck Extension may be used on a drill chuck at any one time, and BullseyeBore Core Chuck Extensions should NEVER be stacked on a drill chuck. Stacked BullseyeBore Chuck Extensions can lead to potentially unstable and/or unsafe rotation of both BullseyeBore Core and the Chuck Extension(s) on the drill chuck. Further, stacked BullseyeBore Chuck Extensions may also contribute to inaccurately projected alignment patterns on the worksurface.

Chuck Extensions work with most common keyed and keyless drill chucks on commercial drills that can accept 0.5” diameter drill bits. Here is a general list of drill type and drill chuck compatibility conditions for Chuck Extensions


1) The drill chuck has a round, metallic, flat face of greater than or equal to 0.65" diameter

2) The drill chuck has a bit hole of less than or equal to 0.56" diameter and larger than or equal to 0.414"

3) The drill has a maximum RPM is equal to or less than 2500 RPM


Here is a general list of Chuck Extension incompatible drill types and drill chucks:


  1. Chuck Extensions are incompatible with drill chucks that have smaller diameter faces, such as those that require use of a Standard Chuck Guide. Do not use Chuck Extensions with drill chucks that have smaller diameter faces and/or require use of a Standard Chuck Guide.
  2. Chuck Extensions are incompatible with Hex Shank drill chucks. Do NOT attempt to use Chuck Extensions with Hex Shank drill chucks.
  3. Chuck Extensions are incompatible with pneumatic drills due to the fast rotational acceleration of pneumatic drills and or the smaller diameter faces that are typically incorporated onto pneumatic drills. Do NOT use or attempt to use Chuck Extensions with pneumatic drills.


For more guidance on Chuck Extension compatibility on different drills and chucks, please refer to the BullseyeBore Core Product and Accessory Compatibility Guide in the BullseyeBore Core product page. Further, always read and follow BullseyeBore Core Safety Guidelines before attempting to use BullseyeBore Core or any BullseyeBore Core accessories on a drill or in an actual drilling operation.

No, you do NOT need a Standard Chuck Guide on BullseyeBore Core when using a Chuck Extension. Chuck Extensions connect magnetically to BullseyeBore Core and have an extended ring that inserts into the BullseyeBore Core to prevent displacement between BullseyeBore Core and the Chuck Extension.

Share by: