How to read a core bit spec sheet

Diamond core bit listings are dense with numbers and half-abbreviated jargon, and two bits that look identical in a photo can behave completely differently on the stone. This guide walks the spec fields in the order they matter, so you can tell whether a bit fits your drill, your material, and the hole you actually need to cut. These are the same dimensions we track for every core bit in our catalog.

Diameter — the hole, not the bit

Diameter is the finished hole size the bit cuts, and it's usually the first thing you filter on. Common jobs are faucet and soap-dispenser holes (roughly 1" to 1-3/8"), and larger cutouts for cooktops or fixtures. Sizes are listed in inches, in millimeters, or both — 35 mm is about 1-3/8", 20 mm is about 3/4" — so convert before you assume two listings match. Note whether the number is the cutting diameter (the hole you get) versus the bit's overall body; reputable sheets mean the hole. Diameter also drives almost everything downstream: the bigger the bit, the lower its safe RPM and the more it wants water.

Connection / thread — will it even mount?

This is the field most likely to leave you with a bit you can't use. The connection is how the bit attaches to your tool, and there is no universal standard. The ones you'll see most in stone work:

• 5/8"-11 — the threaded arbor common on angle grinders and many polishers in North America (5/8" diameter, 11 threads per inch, UNC). If your grinder takes standard cup wheels, this is usually it.
• 1-1/4"-7 — a larger threaded connection found on bigger core bits and rigs.
• 1/2" gas (CNC) — the BSP-style thread used on many CNC and bridge-saw spindles and some stationary drilling setups.
• Hex shank — a hexagonal shaft that drops into a keyless drill or impact chuck, typical on smaller dry bits meant for a handheld drill.
• SDS-plus / SDS-max — rotary-hammer connections aimed at concrete and masonry, not countertop finish work.

Match the connection to the tool you own. A 5/8"-11 bit does not thread onto a 1/2"-gas CNC spindle, and no adapter fully cancels the mismatch. When a bit line ships in several thread options, the connection is a per-variant choice — so confirm you're looking at the exact variant, not just the product family.

Bond and segment type — how the diamond is held on

"Bond" is the matrix that holds the diamond grit to the steel body, and it's the biggest driver of how a bit cuts and how long it lasts. You'll see a few systems:

• Vacuum-brazed — diamonds fused to the body in a single hard layer. Aggressive and fast, tolerant of dry use, and forgiving on angle — often chosen for quick, freehand holes where finish matters less.
• Metal / sintered (segmented) — diamond embedded through the thickness of metal segments, so fresh grit is exposed as the segment wears. Generally longer-lived and cleaner-cutting on hard stone, usually run wet.
• Electroplated — a single nickel-plated layer of diamond; inexpensive, but the diamond is gone once that layer wears.
• Resin — a softer bond seen more in finishing than in aggressive coring.

Related is whether the cutting edge is a continuous rim or discrete segments. Segmented edges clear slurry and heat better; continuous or brazed rims can leave a smoother entry with less chipping. Neither is "best" in the abstract — it's a trade between speed, edge quality, and how hard your material is.

Wet vs dry — cooling is not optional

A core bit is rated for wet, dry, or wet or dryuse, and this is a safety and lifespan spec, not a preference. Wet bits need water to the cutting face; running them dry overheats the bond, kills the diamond, and can warp the body. Dry-rated bits are built to shed heat without water but cut slower and dustier, and even many of those last longer with water if your setup allows it. A "wet or dry" rating means the bit tolerates both, but read whether the sheet still recommends water for hard stone. If you're coring engineered stone or quartzite dry, expect shorter bit life regardless of the rating.

Segment height, usable depth, and segment count

These three numbers tell you how much bit you actually get to use. Segment height(in mm) is the depth of the diamond section — roughly the wear budget before the bit is spent; a taller segment generally means more holes over the bit's life. Usable depthis how deep a hole the bit can physically bore, which needs to clear your material thickness plus any backer. Segment count is how many cutting segments ring the edge; more segments can mean smoother cutting, while fewer, taller segments can cut faster. Check usable depth against real jobs: most countertop material is well within range, but stacked or thick material can exceed a short bit.

Max RPM — the number people ignore

Every bit has a maximum safe speed, and it falls as diameter rises — a small bit may be happy at several thousand RPM while a large one wants only a few hundred. Exceeding the rated RPM is how bits fail dangerously, so it's worth matching against your tool's speed, especially on a variable-speed grinder or polisher. If a listing gives no max RPM for a larger-diameter bit, treat that as a gap to verify rather than a green light to run it flat out. When we can't confirm a value from a manufacturer source, we leave it blank rather than guess.

Application — what it's actually built to cut

Finally, the target material: granite, marble, engineered/quartz stone, quartzite, porcelain, concrete, or general stone. A bit tuned for softer marble can glaze or wear fast in hard quartzite, and a concrete-oriented bit may chip a polished countertop edge. Application ties the other specs together — a hard, dense material generally pushes you toward wet use, a durable metal bond, and a conservative RPM. Read this field as the manufacturer's intended use, then sanity-check it against the bond and cooling specs above rather than trusting the headline alone.

Ready to compare real bits side by side? Browse core bits to filter on every field above, and see our methodology for how each spec is sourced and verified.