In short: choose T38 or T45 by matching the complete top-hammer drill string first, then use hole diameter, drilling depth, rod length, rock conditions and rig capability as confirmation checks. Do not switch thread systems simply because a bit diameter appears to fit. The shank adapter, rod, coupling sleeve and bit must belong to the same compatible thread system, and the drill rig or rock-drill manufacturer’s specification remains the primary reference.
For quarry, mining, tunneling and drilling contractors, the practical question is not “Which thread is stronger?” but “Which thread system matches my rig and the holes I need to drill?” T38 and T45 both sit in widely used top-hammer ranges, and manufacturer application windows overlap. That overlap is why a procurement decision based on hole diameter alone can create connection mismatches, poor drilling performance or avoidable downtime.
T38 vs T45: the buyer’s quick answer
| Decision point | T38 | T45 | What the buyer should verify |
|---|---|---|---|
| Thread system | T38 components | T45 components | Existing shank adapter, coupling and bit thread |
| Typical PerfoMax product positioning | Medium top-hammer drilling; underground, tunneling and quarrying | Heavier surface top-hammer drilling; mining and quarrying | Current rig, application and required hole range |
| PerfoMax listed hole range | 64–89 mm | 89–127 mm | Treat these as product-specific application ranges, not universal thread limits |
| PerfoMax listed rod lengths | 3050, 3660, 4270 and 4880 mm | 3050–4880 mm | Feed length, handling limits and planned drill-string length |
| Best first question | What thread and rod system is the current rig already designed to run? | Rig model and rock-drill/drifter model | |
Selection rule: existing rig and drill-string compatibility comes first; hole diameter and drilling conditions refine the choice rather than replace the compatibility check.
1. Start with the rig, rock drill and shank adapter
A top-hammer drill string is a connected system. Impact energy and rotation are delivered from the rock drill through the shank adapter and then through the rod string to the bit. Sandvik, for example, lists shank adapters in thread families including T38 and T45, while its drill rigs and rock drills specify which rod systems they are designed to use. This is a useful reminder that the thread designation is not an isolated property of the rod.
Before comparing T38 and T45 rods, identify the equipment already on site:
- drill rig manufacturer and model;
- rock drill or drifter model;
- current shank adapter thread;
- current rod thread and rod type;
- coupling sleeve thread, if extension rods are used;
- bit thread and target bit diameter.
If the current system is T38, buying a T45 rod normally means more than changing one rod. The mating components also have to be checked. If you are replacing an existing rod, the lowest-risk route is to match the established drill string unless the rig manufacturer or a qualified drilling-tool supplier confirms a system change.
2. Use hole diameter as a range check, not the only selector
Hole diameter matters because it affects the bit, drilling load and the size of drill string needed to transmit impact and rotation. But OEM data shows why a simple rule such as “T38 below X millimeters and T45 above X millimeters” is unreliable across all rigs and tool families.
For example, Epiroc’s T drill-string data lists T38 and T45 across overlapping bench, construction and production-drilling applications. Sandvik’s RD921 surface rock drill is specified for T38 and T45 MF rods within the same drill platform, and its DL432i underground longhole rig can use T38, T45 or T51 MF rods within its stated hole range. These are equipment-specific examples, not universal limits, but they demonstrate the key procurement point: the same hole diameter may be achievable with more than one thread system depending on the drill, rod architecture and application.
For PerfoMax’s current threaded extension-rod range, the T38 extension rod is listed for 64–89 mm holes, while the T45 extension rod is listed for 89–127 mm holes. Use those ranges when evaluating these specific PerfoMax products, then verify the complete string against your machine and existing components.
3. When T38 is usually the more natural fit
T38 is generally the first system to evaluate when the existing rig and shank are T38 and the job sits within the machine’s intended medium top-hammer range. In PerfoMax’s current catalog, the T38 threaded extension rod is positioned for underground mining, tunneling and quarrying, with T38 rope-thread connections, central flushing and rod lengths from 3050 to 4880 mm.
T38 is therefore a practical candidate when:
- the rig, shank adapter and bit are already T38;
- the planned holes fall inside the T38 rod’s stated application range;
- the feed can handle the selected rod length;
- extension drilling requires T38 coupling sleeves and the complete string can be matched;
- the buyer wants to replace existing T38 rods without changing the rest of the tool system.
Do not interpret “T38 is the natural fit” as “T38 is always the smaller-hole answer.” OEM ranges overlap, and some equipment can run more than one thread family. The rig specification decides what is technically permissible.
4. When T45 deserves consideration
T45 is the next thread system to evaluate when the drill is designed for T45 and the application requires the corresponding heavier rod system. PerfoMax currently positions its T45 threaded extension rod for large-scale surface drilling in mining and quarrying, with T45 rope threads, central flushing and rod lengths from 3050 to 4880 mm.
T45 deserves consideration when:
- the rock drill or shank adapter is specified for T45;
- the current bit and coupling system are T45;
- the intended hole diameter sits within the T45 product’s application range;
- the job uses longer or heavier extension drilling where the selected rig and drill string are designed around T45;
- a planned change from another thread system has been checked as a complete system rather than as a rod-only substitution.
The important distinction is system fit. A larger thread designation does not automatically mean better drilling. Overspecifying the rod system can be just as unhelpful as underspecifying it if the drill, feed, bit and operating parameters are not matched.
5. Check the complete drill string before placing the order
For extension drilling, thread compatibility must be continuous from the drill to the bit. A buyer should be able to trace the string in sequence:
- Rock drill/drifter → shank adapter: confirm the shank adapter is correct for the machine and its outgoing thread is T38 or T45 as intended.
- Shank adapter → first rod: confirm the rod connection matches the outgoing shank thread.
- Rod → coupling sleeve → next rod: if separate couplings are used, every connection must use the same compatible thread system.
- Final rod → bit: confirm the bit connection and diameter suit the rod system and the drilling application.
- Rod length → feed and handling system: verify physical rod length against the rig’s feed, carousel or handling arrangement.
Sandvik’s published drill and shank data illustrates this system approach: T38 and T45 appear as defined thread options tied to specific rock drills and drilling platforms. Treat the manufacturer’s rig manual or tool recommendation as the final compatibility authority when there is any conflict between a generic thread chart and the machine specification.
6. Five common T38/T45 purchasing mistakes
Choosing by bit diameter only
A hole-size chart can narrow the options, but it cannot tell you whether the rig, shank and coupling are compatible. Use diameter as a confirmation variable after identifying the machine and existing thread system.
Assuming T38 and T45 components are interchangeable
They are different thread systems. A rod purchase should be checked against the shank adapter, coupling sleeve and bit rather than treated as a standalone item.
Using another manufacturer’s application range as a universal standard
Published ranges vary by drill-string family and equipment. Epiroc and Sandvik data show overlapping T38/T45 applications. Compare the range of the actual rod and machine you are buying for.
Ignoring rod length and feed compatibility
A correct thread is still the wrong purchase if the rod cannot be handled by the rig or does not fit the intended drilling sequence. Confirm rod length and the planned number of rods for the target hole depth.
Sending an RFQ without the existing system details
“Need T45 rod” is often not enough for a reliable quotation. The rig model, drifter model, current thread, bit diameter, hole depth and rod length remove ambiguity before production or shipment.
7. T38 vs T45 procurement checklist
| RFQ item | Why it matters | Example of useful information |
|---|---|---|
| Drill rig | Defines feed, handling and supported rock-drill options | Manufacturer + exact model |
| Rock drill / drifter | Primary compatibility reference for shank and drill string | Model number or nameplate photo |
| Existing thread | Prevents T38/T45 connection mismatch | T38 or T45; current part number if available |
| Target hole diameter | Checks bit and rod application range | Diameter in mm or inches |
| Hole depth | Determines string length and number of rods | Typical and maximum depth |
| Rod length | Must fit feed/handling system | 3050, 3660, 4270, 4880 mm or required length |
| Bit and coupling | Confirms end-to-end thread compatibility | Thread, diameter and existing part numbers |
| Application and rock | Provides operating context for the recommendation | Quarry bench, tunnel, underground production; rock type/condition |
| Quantity and destination | Supports commercial quotation and packing planning | Required quantity, country/port and Incoterm if known |
8. What to send PerfoMax for a compatibility check
If you are not certain whether your rig needs T38 or T45, send the information you already have rather than guessing the thread. A useful RFQ package includes the rig model, rock drill/drifter model, current shank adapter and rod information, target hole diameter and depth, preferred rod length, bit or coupling part numbers, and clear photos or drawings of existing connections when part numbers are unavailable.
You can also review the current PerfoMax drill rod collection before submitting a request for quotation. For replacement or mixed-brand equipment, ask for a compatibility check before ordering so the rod can be matched as part of the complete drilling string.
FAQ
Can I replace a T38 drill rod with T45?
Not as a direct rod-only substitution. T38 and T45 are different thread systems. A change requires checking the rock drill, shank adapter, coupling sleeves, bit, feed and the manufacturer’s approved drill-string options. If the rig is already configured for T38, replacing only the rod with T45 will not create a compatible connection.
Is T45 always for a larger hole than T38?
No. T45 is commonly used in heavier top-hammer applications, but published OEM ranges overlap. For example, Sandvik lists equipment that can use both T38 and T45, while Epiroc shows different T38/T45 ranges across its drill-string families. Use the actual rig and tool-family specification rather than a universal diameter cutoff.
What hole sizes do PerfoMax T38 and T45 extension rods cover?
PerfoMax currently lists its T38 threaded extension rod for 64–89 mm holes and its T45 threaded extension rod for 89–127 mm holes. These are application ranges for the specific PerfoMax products; they should be checked against your rig, drifter, bit and full drill string before ordering.
What information is most important in a T38 or T45 rod RFQ?
The highest-value information is the exact drill rig and rock-drill/drifter model, current thread system, target hole diameter and depth, required rod length, bit/coupling details and quantity. If thread identification is uncertain, include existing part numbers and clear connection photos or drawings.
Do rod length and hole depth affect the T38 vs T45 decision?
They affect the overall drill-string selection, but they do not determine thread size by themselves. Longer holes can require multiple rods, compatible coupling sleeves and a rod length that suits the feed and handling system. Thread choice still has to remain within the machine’s approved drill-string configuration.
Technical references
- Epiroc — T drill strings: application areas, rock-drill compatibility, hole ranges and rod options for T-series drill strings.
- Sandvik — RD921 rock drill: an equipment example using T38 and T45 MF rods within the same drilling platform.
- Sandvik — DL432i longhole drill rig: an equipment example supporting multiple MF-rod thread systems in a defined drilling range.
- Sandvik — Top hammer shank adapters: published thread options including T38 and T45.
Last reviewed: August 2026.