Description
RockHound’s ST58 Extension Rods (ST58 Drill Tubes) are purpose-built for underground mining, tunneling, and high-precision long-hole drilling applications where accuracy and service life are non-negotiable.
Every rod is manufactured from ZK22CrNi3Mo (23CrNiMo) high-strength alloy steel — a premium material that delivers superior fatigue resistance and structural toughness compared to standard grades widely used on the market. For an in-depth comparison of why we chose this material, read our professional analysis: Rock Drill Rod Material Comparison: 23CrNiMo vs Sanbar64 .
The ST58 “tube” structure provides significantly higher bending stiffness than conventional solid extension rods, translating directly into reduced hole deviation, faster penetration rates, and lower overall drilling cost per meter.
Features
1. Premium Material Grade
Forged from ZK22CrNi3Mo (23CrNiMo) high-strength alloy steel, the ST58 rod resists breakage and permanent deformation under high-frequency impact loads — even in hard, abrasive rock formations.
2. Precision Thread Processing
Manufactured with state-of-the-art CNC thread processing technology, every ST58 thread is held to tight tolerances for a perfect, repeatable fit. This minimizes energy loss at every connection and extends coupling life.
→ Learn more: The Processing of Thread Rock Drilling Rods
3. 20-Hour Deep Heat Treatment
Every ST58 rod undergoes a rigorous 20-hour heat treatment cycle — far exceeding the industry standard. This process builds a hard, wear-resistant surface layer while preserving a tough, flexible core, resulting in a service life typically 30% longer than conventionally treated rods.
→ Learn more: 20 Hour Heat Treatment In Rock Drilling Tools
4. Superior Hole Straightness
The ST58-D76 tube design provides exceptional rigidity along its full length. In long-hole drilling, this rigidity is the single most important factor in keeping holes on target, reducing re-drilling and explosive misfires caused by hole deviation.
5. Efficient Energy Transfer
The ST58 thread geometry is optimized for maximum stress-wave transmission from the rock drill to the bit. Less energy is lost as heat or reflected wave, which means faster drilling and significantly reduced thread wear over the rod’s lifetime.
Technical Specifications
All ST58-D76-ST58 drill tubes are manufactured to RockHound’s strict internal quality standards. Standard configurations are listed below.
| Product Name | L (mm) | L (ft) | D (mm) | D (inch) | Thread | Product Code | Weight (kg) |
|---|---|---|---|---|---|---|---|
| ST58-D76-ST58 Drill Tube | 1525 | 5′ | 76 | 3″ | ST58 | 2A0-7615-29293 | 34.0 |
| ST58-D76-ST58 Drill Tube | 1830 | 6′ | 76 | 3″ | ST58 | 2A0-7618-29294 | 40.0 |
Custom lengths and configurations are available upon request. Contact RockHound with your site specifications for a tailored quote.
Application
The ST58 drill tube system is designed for demanding applications where straight, deep holes are required:
- Underground Mining: Production hole drilling, medium-to-deep hole blasting in stopes and development headings.
- Tunneling: Long-hole exploration drilling and reinforcement bolt hole drilling in large-section tunnels.
- Bench Drilling: Presplit and production blasting where tight hole spacing demands high hole quality.
- Surface Quarrying: Compatible with heavy-duty hydraulic crawler drills in open-pit and dimension stone operations.
The ST58 system is ideally paired with hydraulic rock drills in the 20–35 kW power class and is compatible with standard ST58 couplings, shank adapters, and drill bits.
Maintenance Tips
Proper maintenance is critical to achieving the maximum service life from your ST58 extension rods. Follow these site-proven best practices:
- Thread Lubrication: Always apply professional-grade thread grease to male threads before each connection. This prevents galling, reduces heat buildup at the joint, and is the single most effective way to extend thread life.
- Regular Thread Inspection: After every shift, inspect threads for signs of cracking, fatigue marks, or excessive wear. A rod that has reached its service limit must be retired immediately — continuing to use a worn rod risks losing the bit downhole.
- Drill Feed Alignment: Ensure the drill feed is precisely aligned with the hole axis before drilling begins. Side loading caused by misalignment is a leading cause of premature rod bending and thread failure.
- Flushing Maintenance: Keep the flushing water or air supply clean and at the recommended pressure. Blocked flushing causes overheating and dramatically accelerates rod wear.
- Proper Storage: Store rods in a dry, covered environment, standing vertically or on proper rod racks. Always use thread protectors to prevent corrosion and impact damage during transport and storage.
How to Choose the Right Drill Rod
Selecting the correct extension rod depends on three primary factors: rock hardness (UCS), drill machine power output, and required hole diameter.
The ST58 drill tube — with its 76 mm outside diameter and hollow tube construction — is optimized for:
- Hole depths exceeding 20 meters where hole straightness is critical
- Hard to very hard rock (UCS > 100 MPa) requiring high rigidity
- Hydraulic drill rigs with sufficient power to drive a 76 mm tube effectively
- Applications where faster flushing (enabled by the larger annular space) is a priority
If you are drilling shallower holes in medium-hard rock, a smaller-diameter extension rod system may offer a better cost-per-meter outcome. If you are drilling exceptionally deep holes in fractured ground, consider whether a guide tube or in-hole guide system should complement your ST58 setup.
Not sure which rod is right for your site? Our selection guide covers all the key variables:
→ What Is an Extension Drill Rod? Types, Materials & Selection Guide
FAQ
The key advantage is the "tube" structure itself. The hollow, thick-walled ST58 tube has dramatically higher bending stiffness (section modulus) compared to a solid rod of similar weight. In long-hole drilling, this translates directly into less hole deviation, better blasting results, and a lower overall cost per meter drilled.
We exclusively use ZK22CrNi3Mo (23CrNiMo) premium alloy steel — a chromium-nickel-molybdenum grade specifically engineered for rock drilling applications. This material provides the optimal combination of high-cycle fatigue resistance, impact toughness, and hardenability. You can read our full material analysis here: Rock Drill Rod Material Comparison: 23CrNiMo vs Sanbar64
Duration matters in heat treatment. Our 20-hour cycle allows heat to penetrate uniformly through the full wall thickness of the tube, creating a hardened case with a consistent, tough core throughout the entire rod — not just at the surface. The result is a rod that resists both surface wear and internal fatigue cracking simultaneously, which in field testing typically yields a service life 30% longer than standard-treated rods.
The ST58 system is designed for hydraulic rock drills in the 20–35 kW class using ST58 thread connections. It is compatible with standard ST58 shank adapters, ST58 couplings, and ST58 drill bits from all major equipment manufacturers. Contact us if you need confirmation of compatibility with a specific drill model.
Yes. RockHound operates as a global B2B wholesaler. We offer volume pricing tiers, OEM/private label services, and can manufacture custom lengths or thread configurations to suit specific drilling conditions. Contact our sales team with your annual volume estimate and site requirements for a tailored proposal.
Standard configurations (5' and 6' lengths) are typically held in stock for prompt shipment. Custom lengths or large-volume orders are produced to order — lead time varies based on specification and quantity. Please contact us directly for a confirmed delivery schedule.