When a drilling crew faces hard granite at a quarry site or fractured rock in an underground mine, the difference between a productive shift and costly downtime often comes down to one component: the
thread button bit. This seemingly modest tool sits at the very front of the drill string, absorbing impact energy and grinding through rock — and choosing the wrong one can mean premature wear, slow penetration, or even a stuck bit that halts the entire operation. This guide walks through the essentials of thread button bits, from thread types and face designs to practical selection criteria, so you can make informed purchasing decisions for your next project.
What Is a Thread Button Bit?
A thread button bit is a type of
rock drilling tool used in top hammer drilling systems. It features a threaded rear shank that screws directly onto a drill rod or shank adapter, and a front face embedded with tungsten carbide buttons. During operation, the drill rig's percussion piston delivers high-frequency impact energy through the rod to the bit, and the carbide buttons crush and chip away the rock. Compressed air or water is forced through flushing holes in the bit face to clear rock cuttings from the borehole.
Unlike
dth drilling tool systems where the hammer sits directly behind the bit inside the hole, top hammer thread button bits receive impact energy from the rig's hammer located outside the hole. This makes thread button bits especially suitable for small to medium-diameter holes — typically ranging from 38 mm to 127 mm — in mining, tunneling, quarrying, and construction anchoring applications.
Understanding Thread Types: R25, R32, T38, T45, and T51
The thread designation on a button bit defines both the connection profile and the hole diameter range it can handle. Selecting the correct thread size is the first step in matching a bit to your rig and application.
R25 Thread
The R25 is the smallest common thread size, designed for light-duty handheld rock drills and small pneumatic drifters. R25 thread button bits typically cover hole diameters from 38 mm to 48 mm. They are widely used in narrow-vein mining, small-scale quarry face drilling, and rock bolt anchoring where compact equipment and maneuverability are priorities.
R32 Thread
The R32 thread is one of the most versatile options in the industry. It supports hole diameters from 45 mm to 76 mm and works with a broad range of hydraulic drifters and pneumatic rock drills. R32 thread button bits are commonly seen in underground production drilling, tunnel development, and medium-scale bench blasting. Their balance of strength and flexibility makes them a go-to choice for contractors who need a single thread type across multiple job sites.
T38 Thread
Stepping up in size, the T38 thread handles hole diameters from 64 mm to 89 mm. These bits are built for heavier hydraulic drifters and deliver more impact energy per blow. T38 thread button bits are preferred for production drilling in hard rock mines, large-diameter tunnel face drilling, and deep bench blasting in quarries. The T38 also offers a retrac (retractable) variant — with extra rear carbide inserts — that helps guide the bit out of fractured or collapsing holes.
T45 Thread
The T45 thread is engineered for demanding drilling conditions in medium to hard rock. It covers hole diameters from 70 mm to 115 mm and pairs with high-power hydraulic drifters on jumbo rigs. T45 retrac thread button bits are particularly effective in broken formations where hole collapse is a risk. The larger thread cross-section provides greater torque capacity and reduces the chance of thread failure under heavy loads.
T51 Thread
The T51 thread is the heavy-duty option for large-diameter holes from 89 mm to 127 mm. These bits are used in the most demanding applications — deep open-pit bench blasting, large-scale underground stoping, and heavy civil foundation drilling. T51 thread button bits are built with a robust body and larger carbide inserts to withstand the extreme impact forces generated by the largest hydraulic drifters.
Face Designs: Flat Face, ｄｒｏｐ Center, and Retrac
Beyond thread type, the face geometry of a thread button bit has a direct influence on drilling speed, hole straightness, and bit life. The three primary face designs are flat face, ｄｒｏｐ center, and retrac.
Flat Face Bits
Flat face thread button bits have a uniform front surface with carbide buttons arranged across the entire face. They deliver consistent impact energy distribution and produce straighter holes in competent, homogeneous rock. Flat face designs are a solid choice for general-purpose drilling in medium-hard formations where hole deviation control is important.
ｄｒｏｐ Center Bits
ｄｒｏｐ center bits feature a recessed center section with a slightly raised outer ring. This geometry concentrates impact energy at the gauge row of buttons, improving penetration rate in hard and abrasive rock. The ｄｒｏｐ center design also helps with bit flushing by creating a natural channel for cuttings removal. These bits are commonly used in granite, basalt, and other hard formations.
Retrac Bits
Retrac (retractable) bits incorporate an extended skirt behind the bit face with additional tungsten carbide inserts on the rear. When the drill string is pulled back, these rear inserts ream and smooth the borehole wall, clearing loose debris and reducing the risk of a stuck bit. Retrac bits are essential for drilling in fractured, jointed, or blocky ground where hole collapse is a constant concern.
How to Choose the Right Thread Button Bit
Selecting the correct thread button bit involves evaluating several factors together. Here is a practical framework for making the right choice.
1. Rock Formation and Hardness
The hardness and structure of the rock dictate the button shape, button count, and face design. Soft and medium-hard formations (shale, limestone, sandstone) can be drilled effectively with fewer, larger spherical buttons on a flat face bit. Hard and abrasive formations (granite, quartzite, basalt) require more buttons with smaller diameters and ballistic or semi-ballistic profiles to concentrate impact energy. Fractured or blocky ground calls for a retrac design regardless of hardness.
2. Hole Diameter and Depth
Match the bit diameter to your blasting pattern, bolt size, or casing requirements. As a rule of thumb, use the R25 thread for holes up to 48 mm, R32 for 45–76 mm, T38 for 64–89 mm, T45 for 70–115 mm, and T51 for 89–127 mm. Deeper holes benefit from larger thread sizes that provide better energy transmission and straighter drilling.
3. Drilling Rig Compatibility
Check your rig's shank adapter or drifter output thread. The thread button bit must match the drill rod thread or the shank adapter thread. Common combinations include R32 rods with R32 bits for medium-duty drilling, and T38/T45 rods with T38/T45 bits for heavy-duty applications. Hydraulic drifters with higher impact power (above 15 kW) generally require T45 or T51 thread bits.
4. Flushing Requirements
Adequate flushing is critical for removing cuttings and cooling the bit face. Thread button bits come with different flushing hole configurations — some have front-facing holes only, while others include side flushing holes for better debris clearance. In wet or sticky ground conditions, look for bits with larger or additional flushing channels. Air flushing is standard for surface drilling, while water flushing is often used in underground operations to control dust.
Thread Button Bits vs. Other Rock Drilling Tools
Thread button bits are part of the top hammer drilling family and serve a different purpose than DTH (down-the-hole) bits or rotary tricone bits. DTH bits are connected to a hammer that sits inside the borehole and are better suited for larger holes (typically above 105 mm) and deeper drilling where energy loss through the drill string becomes significant. Rotary tricone bits use a crushing and scraping action with three rotating cones, ideal for large-diameter oil, gas, and water well drilling. Thread button bits occupy the sweet spot for small to medium blast holes in mining and construction, where their combination of fast penetration, precise hole alignment, and cost-effectiveness offers clear advantages.
Maintenance Tips for Longer Bit Life
Getting the most value from your thread button bits requires attention to a few maintenance practices. Inspect the bit face and thread after each shift for signs of uneven wear, button cracking, or thread damage. A worn bit with flattened buttons reduces penetration rate dramatically and increases the load on the drill rig. Use a button bit grinding tool to restore the original button profile when the flat wear area reaches about one-third of the button diameter. Keep threads clean and apply a thin coat of thread grease before each connection to prevent galling and seizing. Store bits in a dry, protected area to avoid corrosion on the thread surface.
Why Source Thread Button Bits from TY Drill Bits
Xi'an Heaven Abundant Mining Equipment CO.,LTD — operating as TY Drill Bits — has been manufacturing and supplying drilling tools since 2010 from our base in Xi'an, Shaanxi, China. We produce a complete range of thread button bits covering R25, R32, T38, T45, and T51 thread sizes, with diameters from 38 mm to 127 mm. Our bits are available in flat face, ｄｒｏｐ center, and retrac designs to match the full spectrum of rock conditions.
Our manufacturing process uses forged alloy steel blanks that undergo quenching and tempering heat treatment to balance surface hardness with internal toughness. Tungsten carbide buttons are sourced from quality suppliers and precision-pressed into the bit face. CNC thread machining ensures consistent thread profiles and tight tolerances, reducing the risk of thread failure under high-impact loads. We hold ISO9001 certification and offer OEM services to meet custom specifications.
With over 90% of our production exported to international markets, we understand the requirements of global mining, quarrying, and construction customers. Our lead time is typically within 15 working days, and we accept multiple payment methods including L/C, T/T, and PayPal. Whether you need a single trial order of R32-51mm bits for a tunneling project or a container load of T45 retrac bits for a large-scale mining operation, we can deliver.
Looking for Reliable Thread Button Bits?
Contact TY Drill Bits today to discuss your drilling requirements. We offer competitive pricing, fast turnaround, and technical support to help you ｓｅｌｅｃｔ the right
thread button bit for your specific rock conditions. Reach out to Ms. Lucy Li at
Lucy@tydrillbits.com or call
+86 15389082037 for a quotation. You can also browse our full product range at
https://www.tydrillingbit.com/rock-drilling-tool/.
Xi'an Heaven Abundant Mining Equipment CO.,LTD
