Core Bit Sizes & Thread Guide (1-1/4-7 vs 5/8-11)

The Two Thread Standards

1-1/4″-7 is the standard for wet core bits on drill rigs and wet core drills — used for hard, cured, and reinforced concrete. 5/8″-11 is the standard for dry core bits on handheld drills — used for block, brick, and masonry. Adapters let you run one thread type on the other machine.

Choosing Diameter by Application

Match the bit to what is passing through the hole: small bits (1″–2″) for electrical conduit and anchors; mid sizes (3″–6″) for plumbing and HVAC; large bits (8″–14″) for sewer, vents, and core sampling. Remember the hole should clear the fitting, not just the pipe nominal size.

Wet vs Dry

Wet bits last longer, cut faster, and control dust — the choice for hard or reinforced concrete on a rig. Dry bits are convenient for handheld work in softer masonry where water is not practical. See wet and dry core bits.

Accessories That Matter

Stock the right adapters, extensions, and pilot guides so your bits fit your drill and reach depth. Questions? Call our team at (701) 922-1526.

Should I size the bit to the pipe or the sleeve?

To the sleeve, always, plus whatever annulus the detail calls for. Sizing to the outside diameter of the pipe is the commonest ordering mistake on penetrations and the most expensive one to discover on site, because the bit is not wrong by much and it is completely unusable.

Work through it in order: what is being installed, what sleeve or conduit does it sit in, what packing or firestopping goes around that, and what does the drawing specify for the finished opening. The bit size falls out of that sequence, and a bit that is one nominal size too small is a wasted mobilisation rather than a wasted bit.

As a rough orientation only: 1 to 2 inches covers conduit and anchors, 3 to 4 inches suits plumbing waste and floor drains, 5 to 6 inches takes larger sleeves and HVAC, and anything above that moves into structural and drainage work. Confirm against the drawing rather than the guide.

When do you have to move from handheld to a rig?

Sooner than most people expect, and the deciding factor is torque rather than diameter alone.

Handheld drilling is reasonable for small diameters in block, brick and masonry, where the reaction torque stays manageable and a slightly imperfect line is acceptable. A pilot bit keeps the barrel from skating off the mark while the crown establishes its own kerf.

Above roughly 3 inches, or in anything reinforced, use a stand. Larger barrels generate torque that will twist a machine out of an operator’s hands the moment the crown catches, and reinforced concrete catches without warning. The stand also holds the barrel perpendicular through the penetration, which is what produces a hole that actually lines up with a baseplate or a sleeve.

Anchoring the stand

The anchor is the weak point in most setups. Set it in sound material rather than in a patch, and check the column for movement before starting rather than discovering it at half depth. Where anchoring is not possible, a vacuum base is the alternative, never a stand simply resting on its feet.

Related products and guides

Barrels across the full diameter range, and the hardware that makes them fit and reach.

• Wet Core Bit — 1 to 14 inch
• Dry Core Bit — 1 to 6 inch, block and masonry
• Thread adapter, 5/8-11 to 1-1/4-7
• 12 inch extension for deep penetrations
• Pilot bit and centering guide
• All core bits