Fareed Mohmed · Engineering

Coupling Selection Calculator

Rate · Factor · Verify

Enter your application data once: load, shafts and misalignment. The type cards, the filtered list and the recommendation update as you type, with every step shown.

Ratings are catalogue values: MISUMI Malaysia Economy series 2025 (pages 06-026, 06-027, 06-032); SKF couplings catalogue 15822 (grid, gear, laminate disc and flex tyre); and the SKF OK coupling brochure 17372 with the OKFX leaflet (oil-injection keyless couplings). MISUMI prints no service-factor table, so its factors here are the usual generic structure; SKF and OK use their own published factors. Confirm the factor for your machine, and confirm the exact part with the supplier, before ordering.

Start Here: The Selection Process

Eight steps from the application to the part number. Read this once, then use sections 01 to 03 to do it: every step below links to the place where you enter or read it. If you are new to couplings, this page is your checklist.

Define the application

Write down what the coupling must do before you pick anything. Most wrong selections start with a missing fact here.

Machine and driver: what turns what (motor, servo, engine, gearbox)
Power in kW and the running speed in RPM
Duty: continuous, intermittent, or reversing
Environment: heat, dust, water, chemicals; and the space available

What the tool does not ask: duty cycle, temperature, chemicals and space have no input box. Use them to choose the service factor (heavier duty, higher factor) and to judge the final pick in step 8.

Fresher tip: note which shaft the coupling sits on. After a gearbox the torque is higher and the speed lower than at the motor, so use the values for that shaft.

Enter it in section 01 · A Load →

Calculate the design torque

Torque from power and speed is T = 9550 × P(kW) / n(RPM), in N·m. That is the average running value. Real machines start, stall and shock, so multiply by a service factor to get the design torque: Td = T × Sf.

Sf in this tool: you choose the driver and the load character (uniform, moderate shock, heavy shock). Generic factors run from 1.0 (servo, uniform) to 3.0 (single-cylinder engine, heavy shock). SKF machine tables and the OK safety factors (2.25 to 4.0) replace them for those couplings. Section 07 lists every value. Reversing or high-inertia duty has no input: pick the next heavier load character.

Servo axes: enter the peak torque, not the continuous torque.

See Td update live in section 01 →

Check the shafts

Diameter on both sides (they can differ)
Shaft material, which sets how much torque the shaft itself can carry
Shaft end: plain round, or keyed. Keyless clamp and oil-injection couplings need plain; keyed hub couplings need a keyway

Fresher tip: the shaft can fail before the coupling does. Sizes that are too small for the torque are greyed out in the lists.

Enter it in section 01 · B Shafts →

Is misalignment expected?

Two shafts on two machines are never perfectly in line. Ask whether your assembly can hold them aligned and rigid.

No, both shafts sit on one stiff frame and are aligned accurately → a rigid coupling is possible. In this tool the rigid ones are the SKF OK oil-injection sleeve and flange couplings; ordinary sleeve, flange and clamp rigid couplings are not in the data.
Yes, or you are not sure → use a flexible coupling and go to step 5.

Why it matters: a rigid coupling on misaligned shafts pushes the error into the bearings, and they fail early.

Estimate the amount of misalignment

Angular, in degrees: the shaft axes meet at an angle
Parallel, in mm: the axes are parallel but offset
Axial, in mm: the shafts move in and out (thermal growth, end float)

Fresher tip: enter the misalignment your installation can really hold. Entering zero keeps every coupling in play, including the rigid OK ones; a realistic value removes them, as it should for two separate machines. The coupling rating is a tolerance for what is left after a good alignment job, not a target.

Enter it in section 01 · C →

Choose the coupling type

You do not have to pick a type first. Leave section 02 on All types and the sizing decides; the cards show how many couplings of each family pass your numbers. Use this table to understand why the survivors are what they are, or to narrow the list by need.

Main need	Family	In this tool
High torque, zero backlash, precise, high speed	Disc	MISUMI single and double disc, SKF laminate disc
Small servo or positioning axis	Single or double disc, slit	MISUMI Economy
Absorb shock and vibration, tolerate misalignment	Flex tyre, grid	SKF flex tyre, SKF grid
Very high torque in a compact body, heavy duty	Gear	SKF gear (needs lubrication)
Large shaft, keyless, quick to fit and remove, shafts accurately aligned	Oil-injection rigid	SKF OK sleeve and flange
Cheap, simple, low misalignment (jaw, elastomer)	Jaw, elastomeric	Not in the data yet: use the Quick Check in section 04
Electrical isolation	Composite or elastomer	Not in the data yet

Misalignment each family takes (angular, from the data): flex tyre 4° · MISUMI slit and double disc 1–1.5° · gear 1.5° · MISUMI single disc and SKF disc 0.5–1° · grid 0.25° · OK rigid none. A gear coupling is a high-torque choice, not a high-misalignment one.

Go to section 02 · types →

Check the ratings and finalise the size

This is the part the calculator does for you. A coupling stays in the list only if it passes every check:

Rated torque ≥ design torque (with margin)
Maximum speed ≥ running speed
Both shaft diameters fit the bore range, and the shaft end matches (keyed or plain)
Angular, parallel and axial misalignment are within the limits
Torsional windup is acceptable for positioning axes
The shaft from step 3 can carry the design torque of that coupling

Reading the result: the funnel shows how many couplings survive each check, and the eliminated list says why each one failed. That is the fastest way to learn what drives the choice.

Go to section 03 · results →

Finalise and order

Pick the material (steel, stainless, aluminium) for the environment
Choose the supplier and exact part from the part number shown
Check availability, cost and maintenance (lubrication, wear parts)
Confirm with the supplier before ordering. The tool shows what it did not check

See the steps for your pick in section 03 →

Six common mistakes

Skipping the service factorSizing on the average torque. The coupling then fails at start-up or under shock.

Using the motor values after a gearboxThe coupling on the output shaft sees the gearbox ratio in torque.

Forgetting the shaftA coupling can be strong enough while a small shaft shears or twists at the same torque.

Entering zero misalignmentThis hides the real constraint and picks couplings that cannot take the installed error.

Keyed shaft, keyless coupling (or the reverse)The bore and shaft end must match. Check it before the torque rating.

Choosing on torque aloneBore range, speed, misalignment and windup can each rule out a coupling that has enough torque.

Brands that make this product

Filled gold: loaded in this tool and rated from the catalogue. Outlined gold: loaded for part numbers only, not strength-checked. Grey dashed: not loaded yet. Hover a brand for what is loaded.

SKFrated

SKF OKrated

MISUMIrated

KTRnot yet

Rexnordnot yet

Lovejoynot yet

R+Wnot yet

Rulandnot yet

Flendernot yet

Tsubakinot yet

Miki Pulleynot yet

Fennernot yet

Voithnot yet

To use a brand that is not loaded, take the design torque Td from section 03 to that brand’s catalogue and check the rated torque, bore range, speed and misalignment the same way. The Quick Check in section 04 tests any coupling’s rated torque against your design torque.

See every hardware and brand →

Brand names and logos are trademarks of their owners and are shown only to identify catalogues.

Application Data

Everything the selection needs, in one place. Change any value and the type cards and the results below update straight away. Nothing else has to be entered further down.

ALoad

Define the load by Servo: use the peak torque

Transmitted Power, P kW

Shaft Speed, n RPM (maximum running speed)

Driver Type

Driven Load Character

Machine (optional, for the SKF service factor)Picks the SKF service factor for grid, gear, flex and disc couplings (catalogue 15822, tables 9 to 11). Leave it unset to use the generic factor from the driver and load.

BShafts

Driver shaft diameterMotor or driving side

Driven shaft diameterBall screw, gearbox or load side

Shaft material (for the torsion check)Allowable shear stress, a conservative value for a shaft with a keyway or cross hole. Sizes below the minimum are greyed in the lists above.

Driver shaft end

Driven shaft end

CMisalignment and stiffness

Angular misalignmentdegrees

Parallel offsetmm (lateral). Single disc takes none

Axial movementmm (±, thermal growth or assembly)

Max torsional windup at TdMatters for positioning axes

Nominal torque T—

Service factor Sf—

Design torque Td—

Min. shaft Ø—

Passing couplings—

Choose a Coupling Type

Pick a family, or leave it on All types. The number on each card is how many couplings of that family pass every check for the application data above, so you can see at once which families can do the job. Families are grouped by supplier. The SKF grid, gear, disc and flex couplings have keyed bores, so set the shaft ends to Keyway to include them; the SKF OK oil-injection couplings are keyless, so they need Plain shaft ends. Photos are from the MISUMI and SKF catalogues.

Results & Recommendation

The data above is checked against 423 catalogue couplings from MISUMI and SKF. A coupling stays in the list only if it passes torque, speed, both shaft bores, shaft ends, misalignment and windup. Each catalogue uses its own service factor, so the “Required” column is the design torque for that coupling. The lowest-rated survivor is recommended; pick any other row to see its full working.

Steps

Quick Check of Any Other Coupling

Using a coupling from another supplier? Enter its rated torque and it is compared with the design torque Td from Application Data (section 01).

Candidate Coupling's Rated Torque N·m, from the manufacturer's catalog

Result—

Find Coupling Type by Application

Application

Visual Reference — All Coupling Types

Rigid Coupling (Sleeve / Flange)

Two flanges (or a single sleeve) bolted or clamped solidly to both shaft ends, transmitting torque with essentially zero backlash or flex. Demands shafts that are already accurately aligned — any misalignment loads the shafts and bearings directly rather than being absorbed by the coupling.

Flexible Jaw / Spider Coupling

Two claw-like hubs drive an elastomeric spider insert in compression rather than touching each other directly. The rubber or polyurethane spider absorbs shock and minor vibration and is the wear item — cheap and fast to replace without moving either shaft. The general-purpose default for pumps, fans and gearboxes.

Flexible Disc / Diaphragm Coupling

A stack of thin stainless steel discs bolted alternately to each hub flexes to absorb angular, parallel and axial misalignment with no elastomer to wear out and no backlash. Runs true at high speed and holds up well to temperature extremes — common on precision drives and turbomachinery.

Gear Coupling

External gear teeth on each hub mesh with internal teeth in a sleeve; the teeth are crowned so they can articulate slightly to accommodate misalignment while still transmitting very high torque in a compact envelope. Needs periodic lubrication (grease or continuous oil) — the classic choice for heavy industrial drives before flexible-disc alternatives became common.

Grid (Spring) Coupling

A serpentine steel spring grid threads through slots in two opposing hub flanges, flexing to absorb shock and cushion torque reversals while still transmitting substantial torque. More rugged and heat-tolerant than an elastomer spider, at the cost of needing grease and a cover.

Bellows Coupling

A thin-walled metal bellows between two hubs flexes to take up misalignment with essentially zero backlash and very low added inertia — ideal where position accuracy matters more than torque capacity. Torque capacity is modest, so this is a light-duty, high-precision coupling rather than a power-transmission workhorse.

Oldham Coupling

A three-piece coupling: two hubs each with a diametrical tongue drive a floating center disc with two perpendicular slots, which slides to accommodate parallel shaft offset while transmitting torque at a constant angular velocity. Handles parallel misalignment far better than a jaw or disc coupling of similar size.

Fluid Coupling

Torque is transmitted hydrodynamically between two vaned impellers through oil, with no rigid mechanical connection at all — the coupling slips under a stall or overload rather than transmitting a damaging torque spike, and lets a motor start and come up to speed smoothly against a heavy inertial load.

Reference Tables

Driver Type	Uniform Load (fans, centrifugal pumps, light conveyors)	Moderate Shock (reciprocating pumps, machine tools, mixers)	Heavy Shock (crushers, punch presses, reciprocating compressors)
Servo or Stepper Motor (peak torque)	1.0	1.5	2.0
Electric Motor or Turbine (smooth)	1.0	1.5	2.5
Multi-Cylinder IC Engine	1.25	1.75	2.75
Single-Cylinder IC Engine	1.5	2.0	3.0

Typical service factor structure, following the pattern published across coupling and power-transmission-component catalogs — confirm the exact figure for your chosen manufacturer and duty cycle. The servo row is typical practice, applied to the motor’s peak torque.

MISUMI Economy series couplings used by the selector

Part	Type	Length L (mm)	Allowable torque (N·m)	Max speed (rpm)	Lateral (mm)	Angular (°)	Torsional rigidity (N·m/rad)	Axial ± (mm)	Mass (g)	Bore Ø (mm)
E-LMCPS12	Single disc coupling	12.35	0.25	10000	—	0.5	266	0.04	3	3–5
E-LMCPS16	Single disc coupling	17	0.6	10000	—	0.5	510	0.05	7	3–6
E-LMCPS19	Single disc coupling	20	1	10000	—	1	1400	0.09	11	3–8
E-LMCPS20	Single disc coupling	23	1	10000	—	1	1800	0.1	20	3–8
E-LMCPS26	Single disc coupling	25.5	2	10000	—	1	3700	0.14	28	5–14
E-LMCPS29	Single disc coupling	25.7	2.2	10000	—	1	3700	0.18	35	5–14
E-LMCPS32	Single disc coupling	28	6	10000	—	1	5700	0.18	46	5–15
E-LMCPS33	Single disc coupling	28.5	6	10000	—	1	5800	0.18	50	5–16
E-LMCPS34	Single disc coupling	32	6	10000	—	1	8100	0.18	55	5–16
E-LMCPS39	Single disc coupling	34.5	13	10000	—	1	18000	0.23	81	8–19
E-LMCPS44	Single disc coupling	34.5	15	10000	—	1	20000	0.27	99	8–22
E-LMCPS56	Single disc coupling	45	28	10000	—	1	50000	0.36	217	10–32
E-LMCPS68	Single disc coupling	53	60	9000	—	1	70000	0.4	348	12–38
E-LMCPS82	Single disc coupling	68	100	8000	—	1	140000	0.5	689	17–42
E-LMCPW12	Double disc coupling	15.9	0.25	10000	0.03	1	133	0.08	3.7	3–5
E-LMCPW16	Double disc coupling	23	0.6	10000	0.05	1	255	0.1	10	3–6
E-LMCPW19	Double disc coupling	27	1	10000	0.1	1.5	700	0.18	14	3–8
E-LMCPW20	Double disc coupling	28.8	1	10000	0.1	1.5	900	0.2	19	3–8
E-LMCPW26	Double disc coupling	35	2	10000	0.15	1.5	1850	0.3	37	5–14
E-LMCPW29	Double disc coupling	34.3	2	10000	0.15	1.5	1850	0.3	43	5–14
E-LMCPW32	Double disc coupling	41	6	10000	0.18	1.5	2700	0.36	67	5–15
E-LMCPW33	Double disc coupling	40	6	10000	0.2	1.5	2900	0.4	60	5–16
E-LMCPW34	Double disc coupling	45	6	10000	0.2	1.5	4050	0.4	77	5–16
E-LMCPW39	Double disc coupling	50	13	10000	0.24	1.5	9000	0.45	118	8–19
E-LMCPW44	Double disc coupling	50	15	10000	0.24	1.5	10000	0.54	144	8–22
E-LMCPW56	Double disc coupling	64	28	10000	0.27	1.5	25000	0.72	318	10–32
E-LMCPW68	Double disc coupling	75	60	9000	0.31	1.5	35000	0.8	492	12–38
E-LMCPW82	Double disc coupling	98	100	8000	0.55	1.5	70000	0.9	1013	17–42
E-LMPLCN12	Slit coupling	18.5	0.4	10000	0.1	1.5	32	0.2	4.8	3–6
E-LMPLCN16	Slit coupling	23	0.5	9000	0.1	1.5	44	0.2	9.3	3–8
E-LMPLCN20	Slit coupling	26	1	7500	0.1	1.5	110	0.2	16.5	4–10
E-LMPLCN25	Slit coupling	31	2	6000	0.15	1.5	162	0.2	29	5–12
E-LMPLCN32	Slit coupling	41	4	4600	0.15	1.5	228	0.2	56	8–16
E-LMPLCN40	Slit coupling	56	8	3600	0.2	1.5	340	0.2	131	10–20
E-LMPLCN50	Slit coupling	71	15	3000	0.2	1.5	580	0.2	265	12–32
E-LMPLCN63	Slit coupling	90	32	2200	0.2	1.5	840	0.2	562	14–40

Values as printed in the MISUMI Malaysia Economy series 2025 catalogue, pages 06-026, 06-027 and 06-032. Single disc couplings allow no lateral offset. A few printed moment-of-inertia values look inconsistent between neighbouring sizes and are used as printed.

SKF and SKF OK couplings used by the selector

SKF service factors by machine (grid, gear, flex and disc)

Machine	Grid, gear, flex (tables 9, 10)	Disc (table 11)
Agitator, pure liquids	1.0	1.0
Agitator, screw, paddle or variable concentration	1.5	1.5
Fan or blower, centrifugal	1.0	1.5
Blower, lobe or vane	1.25	1.5
Compressor, centrifugal	1.0	1.5
Compressor, reciprocating, 4+ cylinders	1.75	3.0
Conveyor, belt, apron or chain	1.0	2.0
Conveyor, screw or bucket flight	1.25	2.0
Conveyor, reciprocating	1.75	3.0
Cooling tower fan	2.0	2.0
Crusher, ore or stone	2.5	3.5
Pump, centrifugal, constant speed	1.0	2.0
Pump, gear, rotary or vane	1.25	1.5
Pump, reciprocating, 3+ cylinders	1.5	2.5
Extruder, plastic	1.5	2.0
Generator, even load	1.0	1.5
Hammermill	1.75	3.0
Rotary kiln	2.0	2.0
Ball or rod mill	2.0	2.5
Machine tool, main drive	1.5	2.0
Machine tool, auxiliary drive	1.0	1.5
Concrete mixer	1.75	2.0
Vibrating screen	2.5	3.0

Selected lines from SKF catalogue 15822, for an electric motor driver with standard starting torque. SKF says the factor must be increased for internal combustion engines but prints no value; the tool applies the ratio of the generic table for those drivers.

SKF OK safety factor f (Mt max ≥ f × T)

Driver	Uniform load	Moderate shock	Heavy shock
Electric motor, turbine, servo	2.25	2.5	2.75
Multi-cylinder engine	2.5	2.75	3.0
Single-cylinder engine	3.0	3.25	4.0

Upper end of each range printed in the OK brochure 17372. Mt max = π · da² · B · p · μ / (2 · 10³) in N·m with da in mm, B = da, μ = 0.14, and p = 120 N/mm² for OKC or 100 N/mm² for OKF.

Coupling Type	Key Characteristics
Rigid Coupling (Sleeve / Flange)	No misalignment tolerance · Maximum torsional stiffness · Requires precise shaft alignment
Flexible Jaw / Spider Coupling	Moderate misalignment tolerance · Absorbs shock via elastomer insert · Low cost, easy to service
Flexible Disc / Diaphragm Coupling	Zero backlash · Handles misalignment by flexing thin metal discs · Good at high speed
Gear Coupling	Very high torque capacity · Some misalignment tolerance via crowned teeth · Needs lubrication
Grid (Spring) Coupling	Good shock absorption · Moderate misalignment tolerance · Rugged, tolerant of harsh environments
Bellows Coupling	Zero backlash · Very low inertia · Low torque capacity · Precision motion control
Oldham Coupling	Excellent parallel misalignment tolerance · Zero backlash version available · Moderate torque
Fluid Coupling	Smooth, slip-based start-up · Inherent overload protection · No mechanical wear item to replace

Explanatory Notes

How the selector filters couplings

1) Nominal torque T = 9550 P / n, or the torque you enter. 2) Design torque Td = T × Sf. 3) Torque: allowable torque ≥ Td. 4) Speed: your running speed ≤ the coupling’s maximum speed. 5) Bores: both shaft diameters must be in the coupling’s catalogue bore list, and keyed ends need Ø8 or more. 6) Misalignment: your angular, parallel and axial values must each be within the catalogue allowance, and single disc couplings take no parallel offset. 7) Windup: θ = Td / torsional rigidity, shown in arc-minutes and optionally limited. Survivors are ordered by outside diameter, then length, so the first is the smallest.

What MISUMI does and does not publish

The Economy catalogue prints allowable torque, allowable angular, lateral and axial misalignment, torsional rigidity, maximum speed, inertia and mass for the disc and slit couplings only. It gives no service-factor table, no life rule and no speed derating, so those parts of the method are the standard practice described above. The Oldham, jaw and set-screw versions list dimensions and bores but no ratings in this catalogue, so they are not selectable here. The “compensation coefficient” of 1 is printed without an explanation, so the tool checks each misalignment separately and shows the combined use as a caution. Add other suppliers by extending the data table.

What SKF and OK publish, and what this tool does with it

The SKF catalogue 15822 gives rated torque, maximum speed, bore range, mass, and misalignment limits for the grid, gear, laminate disc and flex tyre couplings. Bores are given as a range, so the tool accepts any shaft diameter inside it. All of these have keyed bores. Torsional stiffness is published only for the flex tyre coupling, and inertia only for some sizes, so windup is checked only where the stiffness exists. The OK brochure gives Mt max for each size and shaft diameter; the OK couplings are rigid and keyless, so any misalignment entered will rule them out.

Service factors differ by catalogue

Grid, gear and flex couplings use SKF tables 9 and 10, disc couplings use the higher table 11, and OK couplings use the safety factor f. Choose a machine in section 01 to use the SKF values; without one the generic factor is used for SKF and MISUMI alike. The results show the design torque for each catalogue, and the shaft torsion check uses the design torque of the coupling being tested.

Assumptions made in the SKF data

Grid: the angular limit is 0.25°, the parallel value is the printed operating offset, and the axial value is the gap tolerance; sizes 1210 to 1260 are left out because no misalignment figures were found. Gear: the 1.5° angular limit comes from the catalogue summary, and parallel offset is published only up to size 70. Disc: the angular limit is 1° (W4), 0.7° (W6) or 0.5° (W8); single-pack types allow no parallel offset, and the parallel limit of double-pack types is the shortest spacer length times tan of the angular limit. Flex: the rating is the nominal torque. A “—” in a table means the source does not give the value.

Not in the data

The SKF catalogues also list chain, FRC, jaw, universal joint, floating shaft, spacer and taper-bush couplings, and single-engagement gear couplings. They are not included because their ratings are given in a different form (by size and bush, or by speed and power) and cannot be filtered the same way. Use the Quick Check in section 04 for those once you have the rated torque from SKF.

Torsional windup

A disc or slit coupling twists a little under torque. Windup θ = Td / k, with k the static torsional rigidity. Stiff disc couplings give very small angles. The slit couplings are much more compliant, so on a positioning axis the windup, or the coupling’s effect on servo tuning, may matter more than torque.

Why the service factor exists at all

Nominal torque from power and speed describes the average, steady-state condition — it says nothing about starting torque spikes, cyclic loading from a reciprocating machine, or shock from a crusher or press. The service factor inflates the design torque to cover that gap, the same way a service factor works for a chain drive, V-belt or gear reducer.

Bore and speed still need their own checks

A coupling that passes on torque alone can still fail to fit — its bore range has to cover both shaft diameters (which may differ), and every coupling has a maximum rated speed that drops as bore size increases due to balance and centrifugal stress. Confirm both against the manufacturer's selection chart once a torque-capable type is shortlisted.

Flexible couplings are not a substitute for good alignment

Even a coupling rated for several degrees of misalignment runs cooler, lasts longer and vibrates less the more accurately the shafts are aligned to begin with — the misalignment rating is a tolerance for what's left after a competent alignment job, not a design target.

Related tools

For the shaft this coupling connects to, see the Shaft Design Calculator. For the motor and gearbox on the other side of it, see the Motor & Gearbox Selector and Motor & Gearbox Output Calculator. For a servo axis specifically, the Servo Motor Sizing Calculator checks inertia matching and torque.