thread button bit carbide grade comparison

Every drilling contractor has faced the same puzzle: two thread button bits look nearly identical on the shelf, yet one keeps drilling long after the other has been pulled from the hole. In most cases the difference comes down to a single specification — the carbide grade of the buttons. Carbide grade controls how a bit balances hardness against toughness, and choosing the wrong one is one of the fastest ways to turn a profitable project into a string of premature bit changes. This article compares the carbide grades most commonly used in thread button bits, explains what each grade does well, and gives you a practical framework for matching a grade to your rock conditions.

What Is a Thread Button Bit?

A thread button bit is a rock drilling tool used in top hammer drilling. It connects to the drill rod through a threaded shank — common sizes include R25, R32, T38, T45 and T51 — and carries tungsten carbide buttons on its face. Instead of cutting the rock with sharp edges, the buttons fracture it through repeated impact from the drifter. Because the buttons absorb the full force of every blow, their material quality directly affects penetration rate, service life and cost per meter. That is why the carbide grade deserves as much attention as the thread size or the button shape.

What Is a Carbide Grade?

Tungsten carbide buttons are made by sintering tungsten carbide powder with a cobalt binder. The grade is defined mainly by the cobalt content and the grain size of the powder. Cobalt acts as the binder that holds the hard tungsten carbide grains together. Raise the cobalt content and the button becomes tougher and more resistant to impact, but softer and quicker to wear. Lower the cobalt content and the button becomes harder and more wear-resistant, but more brittle and prone to chipping under heavy impact. Every grade is a compromise, and the right compromise depends on the rock you are drilling.

The Hardness vs. Toughness Trade-Off

The single most important idea in carbide selection is the trade-off between hardness and toughness. Hardness is the ability to resist abrasion — it keeps the button from wearing flat when drilling through sand, gravel or quartz-rich rock. Toughness is the ability to absorb impact without cracking — it keeps the button from chipping when it strikes hard, unyielding rock like granite or basalt. Abrasive formations punish a soft button, while hard formations punish a brittle one. A grade that performs well in a sandstone quarry can fail within hours in a granite mine, and the reverse is equally true. Understanding this trade-off is the key to reading any carbide grade comparison.

Carbide Grade Comparison Table

The numbers tell a clear story: as cobalt content rises, hardness falls and toughness rises. There is no "best" grade on this table — only the grade that best matches the rock you are drilling.

Grade-by-Grade Breakdown

YG6 (6% cobalt). YG6 is the hardest of the common grades. Its high hardness gives it excellent wear resistance, so it holds its button profile for a long time in abrasive conditions. The trade-off is low toughness: under heavy impact, YG6 buttons are more likely to chip or crack. YG6 is a sensible choice for soft to medium-hard, abrasive formations such as sandstone, shale and gravel, where gradual wear — not impact — is the main enemy.

YG8 (8% cobalt). YG8 sits in the middle of the range. It offers a balanced combination of wear resistance and toughness, which makes it the default choice for mixed ground where the rock type changes from hole to hole. Limestone, dolomite and moderately abrasive formations are typical YG8 territory. It is not the best option for extreme abrasion or for very hard rock, but it is the most forgiving grade when conditions are unpredictable.

YG11C (11% cobalt). YG11C is the workhorse grade for hard rock drilling. The higher cobalt content gives it the toughness to survive repeated high-impact blows without chipping, which is exactly what granite, basalt and quartzite demand. The "C" indicates a coarse grain structure that further improves impact resistance. The cost is lower wear resistance, so YG11C buttons wear faster in abrasive ground. For hard, non-abrasive rock, it is usually the right call — and it is the same grade used in carbide cutting tools tips YG11C for button bits.

YG13C (13% cobalt). YG13C pushes cobalt content to 13%, giving the highest toughness of the four grades. It is reserved for the most demanding conditions: extremely hard rock, high-impact percussive drilling, and applications where button breakage is the dominant failure mode. Because it wears faster than lower-cobalt grades, YG13C should be chosen only when impact resistance matters more than wear life.

How to Choose the Right Grade

Choosing a grade is a matter of matching the material to the job. A simple four-step check covers most situations.

Step 1 — Identify the rock. Start with the formation. Is it hard (granite, basalt, quartzite), medium (limestone, dolomite) or soft (sandstone, shale, clay)? Hard rock favors high-cobalt grades; soft rock favors low-cobalt grades.

Step 2 — Assess abrasiveness. Hardness alone is not enough. A rock can be soft yet highly abrasive, like sandstone with a high quartz content. Abrasive ground wears buttons down quickly, so it calls for a harder grade even if the rock itself is not very hard.

Step 3 — Consider impact energy. Higher impact energy from the drifter means more stress on the buttons. If your rig runs at high impact energy, or you are drilling deep holes with long rod strings, lean toward a tougher grade.

Step 4 — Match the thread size. The grade works together with the thread size and hole diameter. Smaller bits on R25 or R32 threads are often used in lighter drilling, while T38, T45 and T51 bits handle larger holes and higher energy. Tell your supplier the thread size, hole diameter and rock type together, so they can recommend a grade that fits the whole system.

Common Mistakes to Avoid

Buying on price alone. Carbide is a small part of the bit's cost, but it determines most of the bit's life. A cheap grade that fails early costs far more in downtime than the saving on the purchase price.

Ignoring abrasiveness. Many buyers match the grade to rock hardness and forget abrasiveness. The result is a tough grade that chips less but wears out quickly in sandy ground.

Using one grade for everything. A single grade across all sites is convenient but rarely optimal. If your jobs vary between hard and abrasive rock, keep both a hard grade and a tough grade in stock.

Overlooking grain structure. The "C" in YG11C and YG13C matters. Coarse grain improves toughness; fine grain improves wear resistance and heat resistance. Check the full grade designation, not just the cobalt number.

Matching Grades to Thread Sizes

Thread size and carbide grade work together. For small-diameter bits on R25 and R32 threads, which are common in drifting and smaller bench holes, YG8 or YG11C usually covers the range of rock types. For larger T38, T45 and T51 bits used in bench drilling, long-hole drilling and tunneling, YG11C is the standard choice for hard rock, with YG13C reserved for the toughest conditions. When you order a thread button bit, specify the thread size, hole diameter, button shape and rock type together, and the supplier can match the grade to the complete application.

Conclusion

Choosing the right carbide grade for a thread button bit is not about finding the "best" grade — it is about finding the best match for your rock. Hard, non-abrasive formations call for tough grades like YG11C or YG13C; soft, abrasive formations call for hard grades like YG6 or YG8; and mixed ground calls for the balanced YG8. By pairing the grade with the right thread size and button shape, you can extend bit life, hold penetration rate and lower cost per meter. If you are unsure which grade fits your project, share your rock type, thread size and drilling conditions with your supplier — a good recommendation starts with good information.