Xi'an Heaven Abundant Mining Equipment CO.,LTD
Thread button bits are the most widely used rock drilling tools in tunnel excavation. Whether for face drilling, roof bolting, or blast hole preparation, selecting the right thread button bit directly impacts advance rates, hole quality, and overall project cost. This guide covers which thread types are best suited for tunneling applications, the factors that govern selection, and how to match bit design to ground conditions.
Tunneling operations demand a range of thread sizes to accommodate different drill rigs, hole diameters, and rock formations. The table below summarizes the most commonly used thread systems in tunneling and their typical applications.
| Thread Type | Typical Diameter Range | Drill Rig Power | Primary Tunneling Use |
|---|---|---|---|
| R25 | 33mm – 45mm | Up to 8 kW | Small-diameter bolting, narrow-heading face drilling |
| R28 | 38mm – 48mm | Up to 10 kW | Bolting, shallow blast holes, confined-space drifting |
| R32 | 38mm – 64mm | Up to 15 kW | Main face drilling, bolting, pattern drilling in headings as narrow as 3.5m |
| R35 | 45mm – 64mm | Up to 15 kW | Medium-duty drifting, fragmentation-prone ground |
| R38 | 48mm – 76mm | Up to 18 kW | Production drifting, deeper blast holes |
| T38 | 64mm – 89mm | 15 – 20 kW | Heavy production drifting, long-hole drilling in competent rock |
| T45 | 76mm – 102mm | 18 – 25 kW | Large-diameter tunnel face drilling, high-power jumbos |
| T51 | 89mm – 127mm | 22 – 30 kW | Large-section tunnel excavation, hard rock production blasting |
Among these, R32 is the most versatile and widely adopted thread system in tunneling worldwide. It is the default choice for drill jumbos such as the Atlas Copco Boomer 281/282 and Sandvik DD210/310, providing the right balance of maneuverability, thread strength, and bit weight. For larger headings and more powerful drifters, T38 and T45 become the standard, while R25 and R28 serve specialized bolting and small-diameter roles.
Selecting the correct rock drilling tool for tunneling is a sequential decision-making process. Each choice constrains the next, so following the right order matters.
The thread size must be compatible with your rock drill's impact power. Running an undersized thread on a high-power drifter leads to premature thread wear, fatigue fractures, and lost drill strings. Conversely, an oversized thread on a low-power rig wastes energy and reduces penetration rate. As a general rule: R32 suits drills up to 15 kW, T38 covers 15–20 kW, and T45/T51 handle 20 kW and above.
Hole diameter is dictated by the blast pattern, tunnel cross-section, and required advance per round. For typical tunneling headings, 43–51mm bits are standard for face drilling, while 64–76mm bits may be used for larger cut holes or burn cuts. The diameter must also fall within the recommended range for the chosen thread type.
The carbide button shape is the single most influential factor for penetration rate and bit life:
The face design of a thread button bit affects hole straightness, flushing efficiency, and penetration behavior:
In fault zones, jointed rock masses, or blocky ground — conditions common in tunneling — a standard bit can jam during extraction as loose rock fragments collapse around the drill string. Retrac button bits solve this problem with a tapered skirt and rear-facing carbide inserts that cut through debris on the way out, preventing stuck drill strings and lost rounds. For tunnels passing through fractured geology, retrac bits are not optional — they are essential.
In abrasive tunneling environments — think sandstone, quartzite, or granite — gauge button diameter is the configuration choice that most directly controls bit life. Moving from 9mm to 10mm gauge buttons on the same-diameter bit can extend the regrind interval by 30–40% in high-silica formations. The larger button retains a viable cutting profile longer as it wears, meaning fewer bit changes per shift and higher overall advance rates.
Key takeaway: For abrasive tunnel faces, specify spherical carbide buttons with YG11C-grade carbide and gauge buttons of 10mm or larger. This combination provides the impact toughness required for high-frequency percussive drilling without sacrificing wear resistance.
Getting full value from a thread button bit requires disciplined maintenance. Two rules should guide every tunneling operation:
Xi'an Heaven Abundant Mining Equipment CO.,LTD (TY Drill Bits) has been supplying high-quality rock drilling tools since 2010. Based in Xi'an, China, the company offers a comprehensive range of thread button bits covering R25, R28, R32, R35, R38, T38, T45, and T51 specifications — all manufactured under ISO 9001 quality standards. With 91% or more of production exported to international markets, TY Drill Bits understands the demanding requirements of tunneling projects across diverse geological conditions.
Key advantages of choosing TY Drill Bits for your tunneling needs:
For more details on the complete product range, visit the thread button bit category page or browse the full rock drilling tool catalog.
The right thread button bit for tunneling depends on drill rig power, hole diameter, rock hardness, and ground conditions. R32 is the workhorse of the industry — versatile, standardized under ISO 10208, and suitable for most face drilling and bolting applications. For larger headings and harder rock, T38 and T45 step up to handle the increased loads. In fractured ground, retrac designs prevent costly jamming. Regardless of thread type, matching button shape, gauge size, and face design to the rock is the key to maximizing advance rates and minimizing cost per meter. TY Drill Bits offers a complete range of thread button bits engineered to meet these demands, backed by over a decade of manufacturing experience and a commitment to international quality standards.
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