Kelly Bar Manufacturer
Custom-engineered Kelly Bars for interlocking, friction and multilock duty, drawn against your rig and proven to 143 m.
Selection Tool
What Size Kelly Bar Do You Need?
Outer diameter is driven by rig torque; depth is driven by section count and length. Start here, then confirm with our engineers.
Build Your Enquiry — We Size It Against Your Rig
A Kelly Bar is never sized from depth and ground alone. Rig model, rotary head interface, crowd system and tool weight all change the answer. Tell us about your machine and your job — we translate it into a drawing and a firm proposal.
Why we ask for the rig model: two rigs with the same torque rating can need different bars, because the square box, the drive key layout and the crowd system are not the same. Give us the model and we check our drawing library first — in many cases we have already built that bar.
Please enter your rig model — without it we cannot check the interface.
Why The Rig Matters
The Same Depth Can Mean Three Different Bars
Depth alone does not select a Kelly Bar. These three rigs all drill to roughly 60 m — and each takes a different bar.
Rig torque sets the outer diameter
A 220 kN·m rig and a 400 kN·m rig drilling the same 60 m hole do not use the same bar. Torque decides how much steel the section needs.
- ~220 kN·m → Ø394 class
- ~360 kN·m → Ø508 class
- ~600 kN·m → Ø630 class
Depth sets how many sections, and how long
Reachable depth is a function of section count and the length of each section — not of the diameter alone.
- More sections = more depth, but each joint is another load path
- Longer sections = fewer joints, but higher transport and handling demands
- SW standard: 3 to 8 sections, 9–28 m each
Ground decides how the load is transferred
Rock needs positive mechanical locking. Soil is faster with friction drive. Mixed ground often justifies a combined bar.
- Hard rock → interlocking (SW/JS), locking steps carry crowd force
- Soft soil → friction (SW/MZ), smooth and quick
- Mixed → combined sections
Main Features
What Is The Kelly Bar Main Features?
1
Engineered key drive system
Six keys distribute torque and crowd load. Fitted as standard on both interlocking and friction bars.
2
Alloy seamless tube
Main sections in alloy seamless steel; small diameters heat-treated above 800 MPa.
3
Heat-treated drive keys
Alloy steel keys, secondary heat treatment for hardness plus toughness and weldability.
4
Ultrasonic inspection
Critical welds inspected with recordable ultrasonics, not just visual checks.
5
100% telescoping test
Every bar is fully extended and retracted before it leaves the workshop.
6
Traced quality file
Each bar gets a number; inspection records and photos are archived against it.
Our Products
SW800 — The Tube Behind The Rating
A Kelly Bar is only as strong as the tube it is built from. SW sources seamless alloy tube to a specification we call SW800, verified against GB/T 17396 before it ever reaches the welding line.
YS
Yield strength
≥ 835 MPa
Measured minimum yield (Y.S. 800+ MPa class) — the point at which the tube stops returning to shape.
TS
Tensile strength
≥ 980 MPa
The load the tube takes before it parts. The gap between yield and tensile is the safety margin your operators work inside.
GB
Standard
GB/T 17396
The national standard for seamless steel tubes — every heat is certified and traceable to its batch.
Why it matters: a bar that yields in service does not fail dramatically — it simply stops holding depth. Tube grade is where that is decided.
Anatomy
Eight Components, One Load Path
Every SW bar is a system of eight engineered parts. Torque travels from the rotary head through each of them in turn — specify one badly and the others carry the penalty. The numbered diagram below is the reference for the eight terms that follow.
How to read it: torque enters at the top (tool joint end, item 8) and travels down through each section in turn. Any single weak item becomes the limit for the whole bar.
1
Steel Tube
The seamless alloy body. Grade selected by diameter and torque class — SW800 for the demanding end of the range.
2
External Bar
The longitudinal drive member that carries torque down the section and transmits it to the one below.
3
Locking Plate
On interlocking bars, the machined step that converts torque and crowd force into positive mechanical drive.
4
Upper Guide Ring
Keeps the sections concentric under load, so the telescoping fit stays true as the bar extends.
5
Drive Shell
The load-transferring interface between sections — where contact pressure is shared across the drive faces.
6
End Joint
Connects the bar to the rig or to the next section; machined to the rig manufacturer’s interface.
7
Wear Plate
Sacrificial protection at the high-wear points. Replaceable in the field, so the tube itself is never the wearing part.
8
Tool Joint
The connection to your drilling tool — bucket, auger or core barrel — matched to your kelly box size.
Send us your rig model and we will confirm the tube grade, the drive layout and the joint interface before a single tube is cut.
Definition
What Is A Kelly Bar?
Our Products
A telescopic square or keyed shaft that carries torque and crowd force
A Kelly Bar is the telescopic steel shaft that transmits the rotary head’s torque and the rig’s crowd force down to the drilling tool. It is made of 3 to 8 nested sections that telescope out as the hole gets deeper and retract for transport.
The bar’s outer diameter is chosen from the rig’s torque; its section count and length set the reachable depth; its key system decides whether the load is carried by mechanical locking (interlocking) or by friction along the
Naming: SW/JS = interlocking (机锁) · SW/MZ = friction (摩阻). Example: SW/MZ630-6×26.5 = friction type, Ø630 mm, 6 sections, 26.5 m per section.
Build Standard
How An SW Kelly Bar Is Built
Structure
- Engineered drive key layout on every bar, including friction bars — this is the main reason SW friction bars outlast ordinary ones
- Interlocking (SW/JS): mechanical locking steps carry torque and crowd force into rock
- Friction (SW/MZ): pressure distributed through the key faces, smooth and fast in soil
- Multilock: rack-type continuous steps, crowd force at almost any rotation angle
- Shock absorber, anti-drop disc, lifting lug and bottom square box dimensioned to your tooling
Material
- Alloy seamless steel tube for the main sections
- Small-diameter tubes use alloy cylinder tube with special secondary heat treatment, strength above 800 MPa
- Drive keys in alloy steel with secondary heat treatment — high hardness with retained toughness and weldability
- Wear-resistant key surfaces to keep the telescoping fit tight over years
Manufacturing
- Automated welding robot line plus 30+ experienced welders
- Key welding followed by stress-relief and secondary heat treatment
- Machining of locking steps and square box on CNC equipment
- Shot blasting and industrial anti-corrosion coating before assembly
Inspection
- Incoming material: universal testing machine, impact test, Leeb hardness
- Three-inspection system through the whole process
- Ultrasonic inspection on critical welds, results recorded
- 100% telescoping test — every bar extended and retracted before delivery
- Quality file archived by bar number, traceable for the life of the bar
Specification
Kelly Bar Specification (SW Manual)
Outer diameter, section options and the depth each diameter can reach. Torque column is the matching rig torque used for selection.
| Outer Diameter（mm) | Sections | Section length（m) | Type | Max torque (kN·M) | Max depth（m) |
|---|---|---|---|---|---|
| 720 | 3–8 | 10–28 | Interlocking / Friction | 800 | 36–158 |
| 630 | 3–8 | 10–26.5 | Interlocking / Friction | 600 | 36–143 |
| 575 | 3–6 | 10–19.4 | Interlocking / Friction | 460 | 36–105 |
| 530 | 3–6 | 10–19 | Interlocking / Friction | 400 | 36–95 |
| 508 | 3–6 | 10–16.5 | Interlocking / Friction | 360 | 36–84 |
| 470 | 3–5 | 10–15 | Interlocking / Friction | 320 | 36–76 |
| 445 | 3–5 | 10–14 | Interlocking / Friction | 280 | 36–70 |
| 419 | 3–5 | 10–13 | Interlocking / Friction | 260 | 36–66 |
| 394 | 3–5 | 10–11.6 | Interlocking / Friction | 220 | 36–58 |
| 368 | 3–4 | 10–12.5 | Interlocking / Friction | 180 | 36–50 |
| 355 | 3–4 | 10–11.5 | Interlocking / Friction | 150 | 36–46 |
| 325 | 3–4 | 10–10 | Interlocking / Friction | 120 | 36–40 |
| 299 | 3–4 | 9 | Interlocking / Friction | 100 | 36 |
Depth ranges are manual limits for standard configurations. Special section lengths and wall thicknesses are available on request.
Types
Interlocking, Friction or Multilock?
Interlocking Kelly Bar (SW/JS)
Mechanical locking steps. Full torque and crowd force into rock. Proven to 143 m.
Product Details →
Friction Kelly Bar (SW/MZ)
Engineered key friction design. Smooth, fast, and far longer-lived than ordinary friction bars.
Product Details →
Multilock / Combined Bar
Rack-type steps or combined sections for mixed ground and variable depth.
Product Details →
Shipping & Buying
How To Buy A Kelly Bar From China
1
Send rig & job data
Rig model, hole diameter, required depth, ground conditions and port.
2
Get drawings
We issue a proposal with model, sections and interface drawing for your approval.
3
Confirm & produce
Standard lead time about 7 days from approved drawing, thanks to 13,000 t of tube stock.
4
Inspect & ship
Telescoping test, photos and quality file, then packed and shipped to your port.
Send us your rig model and we will confirm the tube grade, the drive layout and the joint interface before a single tube is cut.
Step 1 — what we need from you to start.
Step 2 — you approve before we cut steel.
Step 4 — packed with the quality file.
FAQ
Kelly Bar Questions We Get Every Week
Can you match my rig exactly?
Yes. Send the rig model and, if possible, a photo of the rotary head and the old bar’s square box. We have interface drawings for Bauer, Soilmec, Casagrande, IMT, MAIT, SANY, XCMG, Zoomlion, Liebherr and CMV rigs, and we draw to your machine where the data is missing.
How deep can a Kelly Bar go?
The SW manual lists 36 m to 158 m depending on outer diameter and section count. Our deepest documented project is 143 m with an SW/MZ630-6×26.5 on the high-speed rail corridor.
Interlocking or friction — which should I buy?
Interlocking (SW/JS) for rock and where you need positive crowd force. Friction (SW/MZ) for soil, sand and clay where speed matters. Mixed ground often uses a combined bar. Our selector tool above gives a first answer.
What is your lead time?
About 7 days for standard configurations because we hold roughly 13,000 tonnes of tube in stock. Custom diameters, special section lengths or non-standard interfaces take longer and are quoted per job.
Do you supply used or refurbished bars?
Yes. SW rebuilt bars are 80–95% new, refurbished to the new-bar enterprise standard, with 500+ sets in stock and a 3-month warranty. See Used & Refurbished.
Keep Reading
Related Pages
Go deeper into the topics most buyers check before ordering.
Extension Bar
Extra length between the rotary head and the top of your Kelly Bar — gain depth without changing the mast.
Interlocking vs Friction
Which type fits your ground
Factory & Capacity
60,000+ m2, two workshops
Quality & Inspection
UT, heat treatment, telescoping test
Projects
143 m HSR, 105 m bridge and more
Customized Service
From rig model to approved drawing
SW Bars In The Workshop
Photo Gallery
Click any frame to see what the shot should show.
Get An Accurate Quote For Your Rig
Tell us your rig model, required depth and ground conditions. Our engineers will return a matching Kelly Bar proposal with drawings, normally within 24 hours.