Buyer’s Guide – Drilling Tools

Tricone Bit for Water Well Drilling: How to Pick the Right One

By Windrilling Technical Team – Updated September 2026 – 10 min read

Last month a water well contractor in Tanzania sent me a photo. A 7 7/8 inch tricone bit, three cones, sealed bearings, every insert flattened almost to the cone body. He had drilled 190 metres with it. His message said the bit was junk.

It was not junk. It was a bit that had been fed twice the weight it was built for, in rock it was never matched to, with no sharpening check for six weeks. He bought a cheap replacement from the same trader. It failed in the same formation in eleven days.

That is the trap behind tricone bit for water well drilling. The bit is not chosen by price per piece. It is chosen by the code on the cone, the bearing inside it, the thread on the pin and the rock it will turn in. Get those four right and the bit pays for itself. Get one wrong and you will blame the supplier for a decision you made.

Below is how we walk buyers through it, in the order that actually matters.

1. What a Tricone Bit Is Doing Down There

Three cones on bearings, rotating as the string turns. The teeth or inserts crush and chip the formation in a rolling pattern. Mud or air carries the cuttings up the annulus. That is the whole machine: rotation, weight and fluid.

A tricone is a rotary tool. It does not hammer anything. That single fact decides where it belongs – and where it does not. In soft to medium formations with interbedded layers, it is forgiving and cheap per metre. In hard, abrasive granite it simply crawls, and a down-the-hole hammer will beat it every shift. We covered that trade-off in detail in DTH vs rotary water well drilling.

2. Reading the IADC Code Before You Read the Price

Every roller cone bit carries a four-digit IADC code stamped on the cone or on the certificate. It is the fastest way to know whether the bit in the photo is right for your hole. You do not need to memorise the table. You need to know what each digit is telling you.

Digit	What it describes	What it tells you on site
1st	Bit series and cutting structure family	Low numbers are steel (milled) tooth for soft ground; higher numbers are tungsten carbide insert (TCI) for harder rock. Published classifications split roughly at 1-3 for steel tooth and 4-8 for insert bits.
2nd	Formation hardness / design group	How hard and abrasive the bit expects the rock to be. A code built for soft shale will not survive a basalt flow.
3rd	Bearing type, seal and gauge protection	Where the money is. Open roller bearing versus sealed bearing, and how much gauge protection is built into the cone edge.
4th	Cutting structure features	Insert shape and spacing – the difference between fast in soft rock and durable in hard rock.

IADC code references are published by the International Association of Drilling Contractors and reproduced across bit manufacturers’ catalogues. Read the code against your supplier’s own chart – the grouping logic is standard, the exact boundaries are not identical between manufacturers.

Here is the practical habit. Before you accept a quote, ask for the IADC code of the bit being offered and the formation you told them about. If the supplier cannot answer both in one message, you are buying from a trader, not a bit supplier.

3. Bearing Type: Where Cheap Bits Hide Their Cost

Two bits can carry the same diameter and the same IADC first digit and still differ by a factor of two in life. The bearing is why.

• Open roller bearing. Cheapest. Fluid flushes the bearing directly, which is fine with clean water-based mud and shallow, soft holes. Abrasive cuttings will eat it.
• Sealed roller bearing. Grease stays in, cuttings stay out. The default choice for water wells with mixed geology and long rotating hours.
• Sealed journal bearing. The heavy-duty option – more contact area, better at high weight on bit and in hard, abrasive formations. Costs more, and is still the cheaper decision over a full campaign.

I asked a Nigerian contractor once why he kept buying open-bearing bits for a hole full of sharp gravel. His answer was honest: “The sealed ones cost double.” He was replacing open-bearing bits every 60 to 80 metres. The arithmetic was not close.

4. Sizes and Pin Threads for Water Wells

Water well work lives in a narrow band of diameters compared with oil and gas. Most of the world’s boreholes are drilled between 6 inch and 12 1/4 inch, and the pin thread has to match the drill pipe already sitting in your yard.

Common water well size	Typical API pin connection	Where it is used
6″ – 6 1/2″	2 3/8″ API REG	Small rotary rigs, domestic and village boreholes, wireline-instrumented holes
7 7/8″ – 8 1/2″	3 1/2″ API REG	The workhorse size for municipal and irrigation wells
9 7/8″ – 10 5/8″	4 1/2″ API REG	Large-diameter production wells, gravel pack completions
12 1/4″ and above	4 1/2″ – 6 5/8″ API REG	Surface hole, casing shoe runs, big irrigation schemes

Pin connections listed above are the common pairings for air and mud rotary water well work. Confirm the thread form – REG, IF and the various metric forms are not interchangeable – and check it against your drill pipe chart before ordering. If you are still building your string, start with drill rod sizes and thread types.

One order detail worth double-checking: whether the bit is offered as a new bit or a re-tipped body. Re-tipped bits can be a legitimate way to hold cost down on a soft formation job. They are not the same product, and a quote that does not say which one it is should be sent back.

5. Milled Tooth or Tungsten Carbide Insert

This is the choice most buyers make by accident, because the cheap bit on the shelf is usually the milled tooth one.

• Milled (steel) tooth. Teeth are machined from the cone steel. They cut fast in soft clay, sand, shale and chalk, and they are cheap. They wear quickly in abrasive ground, and they cannot be re-tipped.
• Tungsten carbide insert (TCI). Carbide buttons pressed into the cone. Slower in soft ground, far longer life in limestone, dolomite and hard sandstone. Re-tippable in most workshops.

A rough rule from our own job files: if the formation changes more than twice down the hole, you will end up running TCI. Soft-ground milled tooth bits are a tool for known, consistent geology, not for a first hole in a new area.

6. Matching the Bit to the Formation

You cannot pick a bit from a brochure alone. You need three things: the hardest formation in the interval, the total depth, and whether you are drilling with air or mud.

Formation in the hole	Bit direction	Why
Clay, sand, gravel, soft shale	Milled tooth, open or sealed roller bearing	Fastest penetration per dollar; abrasion is low so steel teeth survive
Mixed layers, sand over limestone	TCI, sealed roller bearing	Handles the change without a trip; sealed bearing keeps grit out
Limestone, dolomite, medium sandstone	TCI, sealed roller or sealed journal	Insert life matters more than raw speed
Hard abrasive granite, quartzite, basalt	Reconsider the method entirely – a DTH hammer will normally win	A tricone in granite means low metres per bit and high cost per metre

If your hole ends in hard rock but starts in overburden, the usual solution is two strings: rotary tricone through the soft section, then a hammer or a different bit design for the basement. Changing tools is cheaper than burning bits. Our DTH hammer and drill bit selection guide covers the percussion side of that decision.

7. Operating Parameters: the Part the Bit Supplier Cannot Set for You

This is where most of the bits I get photos of were destroyed.

Published distributor guidance for roller cone bits commonly sits in the range of roughly 1,500 to 6,000 pounds of weight per inch of bit diameter, with rotary speeds from about 140 RPM in soft ground down to 40-55 RPM as the rock hardens. Sealed-bearing insert bits are usually pushed toward the heavier end of that weight range and the slower end of the speed range. Large-diameter bits go slower still – listings for 16 inch tricones quote 80 to 150 RPM with weight on bit in the tens of thousands of pounds.

Treat those numbers as a starting envelope, not a prescription. They come from distributor catalogues, and every manufacturer publishes its own chart for its own design. What matters is that you have a number. “As much as the rig will push” is not weight on bit. It is a bit budget running on a timer.

Two things to check on the rig side while you are at it. First, cuttings must be leaving the hole – if the return is sluggish, the bit is regrinding its own debris and every insert is paying for it. Second, the string must be stable. Wobble on a roller cone bit is not a cosmetic issue; it is a gauge-wear generator.

8. Tricone vs DTH Hammer for Water Wells

Short version, because this question comes up in almost every enquiry:

Question	Tricone (rotary)	DTH hammer
Ground it likes	Soft to medium, interbedded, gravel and clay	Hard, abrasive, competent rock
What it needs from the rig	Torque, rotary speed, fluid for cuttings	High-pressure air – compressor sizing drives everything
Straightness	Good, with correct weight and stabilisation	Very good in hard rock
Cost profile	Low tool cost, more metres per bit in soft ground	Higher tool and air cost, much cheaper per metre in granite

If you are choosing between the two methods rather than between bits, read the DTH vs rotary comparison first, then come back to bit selection. Buying the wrong bit for the right rig is a wasted month. Buying the wrong method is a wasted quarter.

9. Choosing From What We Actually Stock

Our TDS tricone bit range covers the sizes that water well and exploration crews use daily – TCI and milled tooth bodies, sealed and open bearing options, and the API REG pins listed in the table above. They are stocked alongside the rest of the drilling tools line, so a bit, a shank adapter and a set of rods can leave on the same pallet instead of three separate shipments.

Two practical notes from our shipping desk. First, tell us the hole size in millimetres if that is how your crew works – we convert, and we would rather convert than guess. Second, tell us the rock. A bit ordered by diameter alone is a coin toss.

10. FAQ

Can a tricone bit drill through hard rock?

It can, with the right insert grade and heavy sealed bearings – but it will be slow and expensive per metre. In granite and quartzite, DTH is almost always the better method. Tricone bits earn their place in soft to medium formations and in mixed ground.

How long should one tricone bit last?

There is no honest single answer – it depends on formation, weight on bit, speed and fluid. What you can do is establish your own baseline. Log metres per bit in the first week for every bit type you run, and you will know within a month whether a bit change was geology or abuse.

Sealed bearing or open bearing for a water well?

If the hole has sand, gravel or anything abrasive in it, sealed. Open-bearing bits suit clean, shallow, soft drilling where the price difference is the deciding factor – which is a smaller slice of real water well work than the price tag suggests.

What thread do I need?

Whatever matches your drill pipe. Most water well strings in our region run 2 3/8″, 3 1/2″ or 4 1/2″ API REG. Measure the pin you already have or send us the pipe spec – guessing the thread is how a bit ends up sitting in a warehouse for six months.

Can used or re-tipped bits be worth buying?

Sometimes, on short soft-ground jobs where the cost of a failed bit is low. Ask for the IADC code, the bearing condition and the gauge measurement before you pay. A re-tipped body with worn bearings is a short-term tool, not a replacement for a new bit.

Before You Order

Send us four things and you will get a bit recommendation you can defend: hole diameter, the hardest formation in the interval, total depth, and the pin thread on your drill pipe. We will come back with a specific bit, its IADC code and the thread we will cut on it. If a cheaper body would do the job, we will say so – a bit that fails on site costs us more than the margin on an upgrade.