Views: 0 Author: Site Editor Publish Time: 2025-12-05 Origin: Site
You measure your anchor, pick a diamond drill bit that "looks about right," drill the hole… and the plug is either too loose, too tight, or the tile cracks. Sound familiar? Choosing the wrong diamond drill bit size is one of the most common—and expensive—mistakes in tiling, stonework, and concrete drilling.
The problem is that bit sizing sounds simple ("8 mm screw = 8 mm bit"), but in reality you have to consider the hardware, the material, the clearance, and even how much chipping you expect at the edge of the hole. With today's harder porcelain, thicker sintered stone, and high-end granite and marble countertops, size accuracy has become more critical than ever.
In this post, you'll learn exactly how diamond drill bit sizing works and how to avoid guesswork. In this post, we'll discuss what those millimeter and inch markings really mean, what factors determine the ideal diamond drill bit size, step-by-step selection methods, recommended sizes for common applications (with tables you can actually use on site), and practical tips to avoid costly sizing errors.
If you're in a hurry, here's the core idea:
The "right" diamond drill bit size depends on:
The hardware size (anchor, screw, pipe, faucet, fitting).
The material (porcelain, dekton, granite, marble, glass, concrete, etc.).
The clearance you need (tight fit vs. loose pass-through).
The thickness and chipping behavior of the surface.
As a quick rule of thumb:
For plastic wall plugs / expansion anchors, choose a diamond drill bit that matches the plug's recommended hole size on the package (often plug diameter + 0–1 mm).
For through-holes (for pipes, cables, faucet bodies), choose a diamond drill bit that is 1–4 mm larger than the outer diameter of the item passing through.
For glass and porcelain, always add a bit more safety clearance because tiny chips can reduce the effective opening.
When in doubt:
Test on a scrap piece with the same material and thickness.
Keep a small range of diamond drill bit sizes (e.g., 6–12 mm) ready to fine-tune the fit.
The rest of this article will show you how to apply these principles in real jobs so every diamond drill bit hole is the size you actually need—not just what's printed on the package.
Before you choose any diamond drill bit, you need to understand what the dimensions actually refer to and how they relate to the final hole.
Most diamond drill bit sizes are given as the outer diameter (OD) of the cutting edge:
Metric sizes: 5 mm, 6 mm, 8 mm, 10 mm, 12 mm, 20 mm, 35 mm, etc.
Imperial sizes: 1/4", 3/8", 1/2", 3/4", 1", etc.
On many vacuum brazed or sintered diamond drill bit designs, the OD is what determines the approximate hole size. However, actual hole diameter can end up slightly larger due to:
Drill wobble or run-out
Material hardness and micro-chipping
Operator technique (angle, pressure, speed)
So a 10 mm diamond drill bit might create a 10.2–10.5 mm hole in practice.
If you work in mixed markets, this basic conversion table is useful when selecting a diamond drill bit:
| Metric Size (mm) | Approx. Imperial | Typical Use Case |
|---|---|---|
| 5 mm | 3/16" | Small plugs, light hardware, anchors in tile |
| 6 mm | 1/4" | Common wall plugs, light fixtures |
| 8 mm | 5/16" | Heavier plugs, brackets |
| 10 mm | 3/8" | Medium anchors, shower bars, grab bars |
| 12 mm | 1/2" | Larger anchors, some pipe penetrations |
| 20 mm | ~3/4" | Faucet holes, cable grommets, small pipe penetrations |
| 35 mm | ~1-3/8" | Kitchen/bath faucets, some mixer bodies |
| 45–60 mm | ~1-3/4"–2-3/8" | Waste outlets, some sink accessories |
| 68–80 mm | ~2-11/16"+ | Electrical boxes, larger pipe openings in lightweight walls |
Having a set of diamond drill bit sizes that covers these ranges allows you to handle most residential and commercial drilling tasks.
There are two main geometries:
Core diamond drill bit (hole saw style):
Hollow center, cuts a ring. Ideal for larger holes (e.g., 20–80 mm).
Solid diamond drill bit (tapered or cylindrical):
Solid tip. Better for smaller diameters (e.g., 5–12 mm) and precise anchoring holes.
On product category pages from professional suppliers, you'll often see sets of small vacuum brazed diamond drill bit sizes (5–18 mm) and larger diamond core drill bit ranges (20–150 mm) for different materials like porcelain, granite, marble, dekton, and concrete.
Both count as a diamond drill bit, but their sizing and applications are quite different.
Selecting the right diamond drill bit size is not just reading one number. You must balance several factors.
The most important starting point is what will go through or into the hole:
Expansion anchor / wall plug
Screw or threaded rod
Pipe / conduit
Faucet body / mixer
Cable bundle / grommet
Typically, the manufacturer of the hardware will specify a recommended hole size. For example:
8 mm plastic plug → 8 mm diamond drill bit
M10 anchor → often requires 12 mm diamond drill bit (for sleeve type)
Always check the packaging; if it shows "Drill: 10 mm", that is the bit size you should start with.
A hole in porcelain behaves differently from a hole in concrete:
Porcelain / ceramic / dekton / sintered stone
Very hard, brittle surface → more prone to edge chipping.
Often needs a bit more clearance to account for micro-chips.
Granite / marble / natural stone
Hard but more forgiving than porcelain; still requires precise diamond drill bit control.
Concrete / reinforced concrete / brick / block
Softer than porcelain at the surface, but may have aggregates and steel inside.
For brittle materials, it's safer to oversize the diamond drill bit slightly (e.g., +1 mm) to prevent tight fits that stress the material.
Ask yourself: Should this be a tight fit or a loose pass-through?
Tight fit (e.g., expansion anchors)
Hole size ≈ plug specification; usually no extra clearance.
Pass-through (e.g., faucet body, cable, pipe)
Hole size > outer diameter of object, usually +1–4 mm depending on application.
For example:
A 35 mm faucet body may need a 35–37 mm diamond drill bit hole in stone or porcelain countertops, so that there's room for installation and sealant.
Thicker materials and multi-layer systems affect the effective size:
Thick granite or marble slabs can produce more side friction over depth.
Tile over concrete: the diamond drill bit must pass through both materials, and any misalignment increases effective hole variance.
The thicker the material, the more carefully you should test with the chosen diamond drill bit size before cutting the final workpiece.
Here is a practical workflow you can follow on every job.
Start with the accessory or hardware:
Read the packaging: "Requires 8 mm hole", "Drill size: 10 mm", etc.
If not available, measure the outer diameter with calipers.
For example:
Wall plug: OD 8 mm → likely an 8 mm diamond drill bit.
Pipe: OD 25 mm → you probably want a 26–30 mm diamond drill bit for pass-through.
Ask:
Is this expansion anchoring (tight fit) or a clearance hole (loose)?
Will there be sealant, gasket, or trim cover that can hide a slightly larger hole?
Tight fit → match plug/anchor size.
Clearance hole → add 1–4 mm to the hardware's outer diameter.
Now adjust based on the material:
For porcelain, dekton, sintered stone, glass:
Add 0.5–1 mm extra bit size compared to the hardware, because minor chipping can reduce the usable opening.
For granite & marble:
Often hardware OD + 1–2 mm is enough for clean installation.
For concrete:
For anchors, follow manufacturer's drill size exactly with a quality diamond drill bit or dedicated concrete bit.
Look at what you have in your kit:
Do you have a diamond drill bit exactly matching the needed size (e.g., 8 mm, 10 mm, 12 mm)?
Or do you only have a set with 6 mm, 8 mm, 10 mm, 12 mm, 20 mm, 35 mm, etc.?
If you don't have the perfect size, choose the closest diamond drill bit and test it on scrap material.
Before drilling the visible surface:
Take a scrap tile, leftover stone piece, or a hidden corner.
Drill a hole with the chosen diamond drill bit.
Test-fit the plug, screw, pipe, or faucet.
If the fit is too tight, move up one size in your diamond drill bit range. If it's too loose, consider whether this is acceptable (often yes for pass-through holes with trim rings or covers).
Below is a practical reference table. Always verify with your hardware supplier, but this will give you a strong starting point for choosing the right diamond drill bit size.
| Application | Plug / Anchor Type | Recommended Diamond Drill Bit Size |
|---|---|---|
| Light accessories (towel hooks, soap dishes) | 6 mm plastic wall plug | 6 mm diamond drill bit |
| Medium accessories (towel bars, shelves) | 8 mm plastic wall plug | 8 mm diamond drill bit |
| Heavy items (grab bars, large shelves) | 10 mm heavy-duty plug | 10 mm diamond drill bit |
| Structural fixings (handrails, brackets) | M10 mechanical anchor | 12 mm diamond drill bit (typ.) |
For porcelain and glass, if you see significant chipping, you can try adding 0.5–1 mm to the diamond drill bit size and relying on larger washers or trims to cover the edge.
| Fixture Type | Typical Body OD | Suggested Hole Size (Diamond Drill Bit) |
|---|---|---|
| Single-hole bathroom faucet | 32–34 mm | 35 mm diamond drill bit |
| Kitchen mixer tap | 34–36 mm | 35–37 mm diamond drill bit |
| Soap dispenser or accessory | 24–26 mm | 26–30 mm diamond drill bit |
| RO faucet or small tap | 12–14 mm | 14–16 mm diamond drill bit |
These values assume granite, marble, or engineered stone countertops drilled with a quality diamond drill bit or diamond core drill bit.
| Pipe / Conduit OD | Application | Suggested Diamond Drill Bit Size |
|---|---|---|
| 16–20 mm | Small water pipes, electrical conduits | 22–25 mm diamond drill bit |
| 25–32 mm | Larger water pipes, drain lines | 30–40 mm diamond drill bit |
| 40–50 mm | Waste pipes, HVAC lines | 45–60 mm diamond drill bit |
| 63–75 mm | Main drainage or ducting | 70–90 mm diamond drill bit |
For glass, precision is even more important:
Small hinges / clamp fittings:
Fitting pin 8–10 mm → 10–12 mm diamond drill bit.
Lock cylinders / specialized hardware:
Check OEM cut-out drawings and match diamond drill bit sizes exactly, often using multiple bits to create slots.
For glass, always use quality diamond drill bit sets designed for glass and follow low speed, plenty of coolant, and minimal pressure.
Different diamond drill bit diameters require different technique.
Typical use: wall plugs, light hardware, pilot holes.
Technique tips:
Higher RPM with controlled pressure.
Very stable hand or guide to prevent bit dancing.
Short, frequent pecking to avoid overheating small tips.
Typical use: anchors, cable holes, small faucet or pipe penetrations.
Technique tips:
Mid-range RPM, moderate pressure.
Use a guide or template to prevent walking on smooth porcelain or marble.
Clear debris regularly to maintain speedy cutting.
Typical use: faucet holes, sink and waste holes, pipe penetrations, electrical boxes.
Technique tips:
Lower RPM, higher torque from robust tools (often angle grinder or dedicated rig).
Start at a slight angle to score a groove, then straighten up.
Apply steady but not excessive pressure; let the diamond drill bit segments work.
Cool with water when the bit is rated for wet drilling.
Because large diamond drill bit sizes remove more material, correct speed and cooling make a massive difference in drilling speed and tool life.
Should you buy just the diamond drill bit you need today, or invest in a full set?
Buying just one diamond drill bit makes sense when:
You have a one-off job with a known requirement (e.g., "I need one 35 mm hole for this faucet").
You rarely work with hard materials and don't expect many future projects.
Budget is very limited and you're focused on immediate needs.
In this case, pick a high-quality diamond drill bit rated for your material (e.g., vacuum brazed for porcelain or dekton) and follow all best practices.
A diamond drill bit set is smarter when:
You are an installer, tiler, stone fabricator, or remodeler.
You regularly face unknown on-site requirements ("customer wants an extra hole here").
You handle mixed materials: porcelain, sintered stone, granite, marble, concrete.
A typical useful set might include:
Small bits: 5, 6, 8, 10, 12 mm
Medium bits: 20, 25, 30 mm
Large bits: 35, 40, 50, 60 mm
Many professional suppliers now offer modular diamond drill bit sets (often vacuum brazed with hex shank or M14 threads) that allow you to cover a wide range of jobs from porcelain tile installations to on-site granite modifications.
Yes, a full diamond drill bit set costs more upfront. But:
It reduces last-minute hardware store runs.
It avoids "making do" with the wrong size, which can crack tiles or ruin slabs.
It positions you as a prepared professional, especially in demanding markets using 20 mm thick porcelain slabs and sintered stone.
If drilling hard materials is part of your regular business, a good diamond drill bit set is not an expense—it's a productivity tool.
Even with the right diamond drill bit chart, small mistakes can cause big problems. Here's how to avoid them.
Sometimes the nominal size (for example, "1" pipe") doesn't match the physical outer diameter. Use calipers or a precise ruler and measure the actual OD before choosing your diamond drill bit.
When drilling porcelain, dekton, or sintered stone, tiny chips can reduce the effective opening:
Always drill with a sharp, high-quality diamond drill bit designed for these materials.
Consider adding +1 mm bit size if you know the material chips easily.
Use jigs, templates, and proper speed to minimize chipping.
Due to run-out and drilling motion, the real hole is almost always slightly larger than the diamond drill bit diameter.
Don't oversize too aggressively from the start.
Aim close to the target; you can enlarge a hole slightly if needed (for example by gently tilting the diamond drill bit or using a larger bit to chamfer the entry).
If you frequently install the same brand of faucet, hardware, or anchors:
Record the exact diamond drill bit size that gave the best result.
Note the material type and thickness.
Over time, this becomes your own "sizing Bible" and saves time on every project.
On expensive materials like marble, granite, and large-format porcelain slabs:
Always test the chosen diamond drill bit size on a scrap or off-cut first.
Once you confirm the perfect fit, then drill in the visible area.
This simple step prevents costly replacements and ensures cleaner installations.
Choosing the right diamond drill bit size isn't guesswork or magic—it's a logical process based on hardware dimensions, material behavior, and the type of fit you need.
Start from the hardware's recommended drill size, then adjust for your specific material (porcelain, granite, marble, dekton, glass, concrete) and the desired clearance. Understand the differences between small solid bits and larger diamond core drill bit designs, and keep a versatile range of diamond drill bit sizes in your kit if drilling is part of your daily work.
When you combine the right size with correct drilling technique, you'll:
Get cleaner, more professional holes.
Avoid cracked tiles and damaged countertops.
Reduce callbacks and complaints.
Save time and money on every project.
In short, the right diamond drill bit size turns a risky operation into a controlled, repeatable process—whether you're a DIY user or a professional installer.
Use an 8 mm diamond drill bit unless the manufacturer specifies otherwise. For typical plastic wall plugs, the plug diameter and drill diameter usually match. If you're drilling very hard porcelain, consider testing on scrap first to confirm the fit.
For pass-throughs, choose a diamond drill bit that is 1–4 mm larger than the outer diameter of the pipe or faucet body. For example, a 34 mm tap body might use a 35–36 mm diamond drill bit to allow easy installation and sealant.
Yes, but carefully. You can:
Use the next larger diamond drill bit size and gently re-center over the hole.
Slightly tilt the bit to chamfer and widen the entrance (only if you can hide it with a trim ring).
Always proceed slowly, especially in porcelain or glass.
The nominal sizes are the same, but your choice of diamond drill bit and clearance may differ:
In porcelain, you often need a bit more clearance because of chipping.
In concrete, you follow the anchor manufacturer's size more strictly for load performance.
If you rarely drill hard surfaces, you can buy just the specific diamond drill bit size you need. If you plan multiple projects with different fixtures, a small set (5–12 mm plus one or two larger sizes like 20 mm and 35 mm) offers good flexibility at reasonable cost.
