Direct answer: R38 and T38 are different top-hammer thread systems and should not be connected directly. The shared “38” does not make an R38 rod compatible with a T38 coupling, shank adapter or bit. Before ordering a replacement, identify the complete thread designation at every interface and confirm the rod body, end type, length and flushing passage separately.
This distinction matters when a mine, quarry, contractor or distributor inherits mixed stock, replaces an unmarked rod, or changes suppliers. A mismatched component may start to engage, yet incomplete or incorrect contact can damage both parts, interrupt energy transfer and create a difficult breakout or downhole failure. Do not use a successful hand-start as proof of compatibility.
R38 vs T38: The Buyer-Level Difference
R38 is an R-family connection, commonly described as a rope-thread system. T38 belongs to the T-family and uses a different thread geometry. The code “38” is useful for identifying the nominal size class, but compatibility also depends on the family letter and the supplier’s controlled dimensions.
| Check | R38 | T38 | Buyer conclusion |
|---|---|---|---|
| Thread family | R / rope family | T family | The family designation is part of the specification. |
| Shared number | 38 | 38 | The same number does not mean the profiles mate. |
| Direct interchange | No direct interchange should be assumed | Use components specifically identified for one system. | |
| Items affected | Shank adapter, rod ends, coupling sleeves, threaded bit and any transition component | Verify the complete connection chain. | |
| How to approve | OEM part data, supplier drawing, legible marking, gauge or verified sample | Do not approve from outside diameter alone. | |
Official product literature reinforces the separation. Epiroc publishes R drill strings and T drill strings as distinct systems. Its current pages list an R38 offering and separately list T38 within the T range. Boart Longyear also lists R38 among its underground rod thread options, while Sandvik lists T38 among its current top-hammer shank-adapter threads. These are catalog examples, not universal application rules; the exact rig and drill-string documentation still controls.
Why Similar Outside Diameter Does Not Prove Compatibility
Buyers often measure the largest visible diameter and conclude that two threads are the same. That check is insufficient. Two connections can be close in overall size while differing in flank shape, crest and root form, lead, entry geometry, contact surfaces or manufacturing tolerance. Wear can make the difference harder to see.
The failure mechanism is practical: a wrong male thread may contact only a small part of the wrong female profile. Under percussion and rotation, the load is then concentrated instead of distributed through the intended contact area. A connection may loosen, gall, deform or become impossible to separate. Even if it survives a short test, it has not demonstrated a safe replacement configuration.
Trace the Complete Top-Hammer Connection Chain
A replacement rod is not selected in isolation. In a conventional extension string, compatibility runs from the rock drill through the shank adapter, coupling and rods to the bit. Each interface needs a defined thread on both sides.
| Interface | What to record | Typical ordering error |
|---|---|---|
| Rock drill to shank adapter | Rock-drill make/model, shank part number and spline or chuck interface | Ordering by rod thread while ignoring the machine end. |
| Shank adapter to first rod/coupling | Exact R38 or T38 designation and the required mating end | Assuming any “38 mm” adapter fits. |
| Rod to rod | Thread, male–male or male–female arrangement, coupling type | Mixing an extension rod and speed rod without checking the assembly. |
| Rod to bit | Bit thread, bit type, hole diameter and flushing arrangement | Matching the bit diameter but not its thread. |
| Transition component | Both end specifications, approved drawing and service limits | Calling it only an “adapter” without defining either end. |
PerfoMax’s active T38 extension drill rods are male–male rods that use a separate T38 coupling sleeve. The product page also treats male–female speed rods as a separate quotation configuration. That is a useful reminder: a correct thread name does not finish the specification. End type and string architecture must also match.
How to Identify an Unknown R38 or T38 Thread
Use evidence in descending order of reliability. Start with documentation and component identity, then use dimensional checks. Avoid turning visual inspection into a guess.
- Record the machine and rock drill. Note the rig model, rock-drill model and any shank-adapter part number.
- Clean without altering the thread. Remove grease and loose debris under the site’s approved procedure. Do not grind, file or chase an unidentified connection.
- Find markings. Photograph stamps on rods, sleeves, shank adapters and bits. Include one full-component photo and close-ups.
- Check the purchase trail. Compare the current item with drawings, packing lists, prior part numbers and approved samples.
- Measure methodically. Record major diameter, pitch or lead, threaded length, shoulder geometry, bore and overall end dimensions using calibrated equipment.
- Use the correct gauge. A verified supplier or inspection department can compare the part with the specified profile or master.
- Confirm all mating parts. Do not approve a rod until the coupling, shank adapter and bit are identified too.
For a broader field-identification workflow, see how to identify R32, T38 and T45 threads. When the machine-side component is uncertain, use the shank-adapter compatibility guide to collect the rock-drill, flushing and thread information together.
Can You Use an Adapter Between R38 and T38?
A purpose-designed transition component may exist for a specific drill-string arrangement, but “use an adapter” is not a general compatibility answer. The transition must be engineered and approved for the exact machine, percussion level, rotation, feed, flushing path, rod configuration and application.
Before considering a transition, confirm:
- the exact thread and gender on both ends;
- the component’s drawing, material, heat treatment and inspection basis;
- the internal flushing passage and seal/contact arrangement;
- the added length, outside diameter and clearance through the feed and hole;
- whether the extra interface changes handling, breakout or wear monitoring; and
- whether the rock-drill, rig and tooling suppliers permit the configuration.
A transition does not turn R38 stock into T38 stock. It creates another defined interface that must be managed. If the fleet is changing systems, a controlled conversion plan is usually clearer than allowing undocumented mixed components to circulate.
When Does a Full System Change Make More Sense?
| Situation | Safer decision path |
|---|---|
| One emergency replacement is needed | Source the same verified thread and end configuration as the working string. |
| Both R38 and T38 stock are present | Segregate, mark and inventory the families before issuing tools. |
| The rig has changed shank adapter | Revalidate the adapter-to-bit chain; do not copy the old rod order automatically. |
| A fleet conversion is planned | Define the replacement boundary, remaining stock, training, gauges, spares and phase-out date. |
| Identity remains uncertain | Quarantine the part and verify it against a drawing, gauge or known sample. |
Do not choose R38 or T38 from the letter alone. Published OEM examples associate the systems with different product ranges and applications, but actual selection depends on the rock drill, impact power, hole diameter, depth, rod architecture and OEM recommendations. A current T38 listing is not proof that every machine can be converted to T38.
Common R38–T38 Ordering Mistakes
- Dropping the letter from the RFQ. “38 mm thread” is incomplete.
- Approving from rod-body diameter. Body size and thread family are separate fields.
- Testing a dirty or worn connection by force. Damage can hide the original profile and damage the sample.
- Checking only rods and couplings. The shank adapter and bit remain part of the same compatibility chain.
- Mixing MM and MF terminology. State whether the rod is male–male extension or male–female speed type.
- Using an unverified adapter. Both ends and the service conditions must be defined.
- Copying an old part number without checking the installed rig. Repairs and conversions can change the current setup.
RFQ Checklist for R38 or T38 Replacement Rods
- rig manufacturer, model and serial range if relevant;
- rock-drill model and shank-adapter part number;
- required thread: R38 or T38, stated explicitly;
- photos of the shank adapter, both rod ends, coupling and bit;
- male–male extension rod or male–female speed rod;
- overall and effective length basis;
- round or hex body and body dimension;
- flushing-hole requirement and flushing medium;
- coupling type and outside diameter;
- bit thread and target hole diameter;
- hole depth, drilling direction, rock condition and operating setup;
- quantity, required inspection records, marking, packing and destination.
If an existing T38 string is working correctly, the fastest route is to provide the current rod drawing or sample details rather than rebuilding the specification from memory. The PerfoMax T38 rod page lists quotation lengths of 3,050, 3,660, 4,270 and 4,880 mm, but the approved quotation drawing controls the final length basis, body, flushing passage, end type and inspection scope. For length-specific planning, see the T38 drill rod length guide.
Frequently Asked Questions
Are R38 and T38 threads interchangeable?
No. They are different thread systems. Match the full R38 or T38 designation on the mating components and verify the supplier drawing or gauge.
Why do both names contain 38?
The number identifies a nominal size class, but the leading letter identifies the thread family. Compatibility needs both parts of the designation.
Can calipers alone identify R38 vs T38?
Calipers help document diameter and length, but they do not fully verify thread profile, lead, contact geometry or tolerance. Combine measurement with markings, part data, gauges or a known sample.
Do I need to replace the bit when changing from R38 to T38?
If the bit has an R38 threaded connection, it will not directly fit a T38 string. A conversion review must cover the shank adapter, rods, couplings, bit and any transition component as one system.
What should I send PerfoMax for a compatibility check?
Send the rig and rock-drill models, shank-adapter part number, photos of every connection, current rod dimensions, end type, bit details, hole requirements and any available drawing. PerfoMax can then quote against the documented T38 configuration instead of guessing from appearance.
Confirm the Thread Before You Commit the Order
The safe conclusion is simple: R38 and T38 may look close, but they are not substitute designations. Preserve the letter, verify the entire connection chain and separate thread identity from rod length, body and flushing requirements. For a documented T38 replacement, review the active PerfoMax T38 extension rod options and send the existing system details with your inquiry.