Flexible shaft couplings · Nominal and design torque with service factor, coupling type and insert material, misalignment limits, speed, bore and shaft gap
A shaft coupling joins two shafts end to end — a motor to a pump, gearbox or conveyor — transmitting torque while accepting some misalignment and, in flexible designs, damping shock. Fix three things before ordering: the design torque from the driver's power and speed and the application's service factor, the coupling type and insert material for the misalignment, temperature and environment, and the two bores, keyways and shaft gap.
Flexible and rigid couplings connecting rotating shafts in industrial drives: jaw, disc, diaphragm, beam, gear, grid, tyre and universal-joint types. Clutches, torque limiters, magnetic couplings, fluid couplings and cardan shafts sold as complete driveline assemblies are outside this page; torque limiters and magnetic couplings are separate products.
01
Lovejoy's jaw coupling selection procedure starts with nominal torque — in-lb = HP × 63,025 ÷ rpm, or N·m = kW × 9,550 ÷ rpm — then multiplies it by the application service factor from its Chart 1 to get the design torque, and picks the first coupling size whose rated torque for the chosen insert material equals or exceeds it. It then checks maximum speed for that size and insert and compares the shafts with the maximum bore, moving up a size if a shaft is too large. [1]
Its worked example connects a 20 HP standard electric motor at 1,800 rpm to a rotary pump: nominal torque is 700.28 in-lb, the service factor for an electric motor with standard torque driving a rotary pump is 1.25, design torque is 875.35 in-lb, and the first NBR size to cover it is the L150 with a nominal rating of 1,240 in-lb, whose 5,000 rpm limit with NBR is above the motor's 1,800 rpm. [1] Lovejoy's selection worksheet asks for the driver type, power, speed, both shaft diameters and keyways, usable shaft lengths and the distance between shaft ends. [2]
Lovejoy lists its jaw couplings in 24 sizes from 0.4 N·m to 19,209 N·m with bores of 4.45 to 178 mm. [3]
Editorial calculation: in metric, a 15 kW motor at 1,500 rpm gives 15 × 9,550 ÷ 1,500 = 95.5 N·m nominal; with the same 1.25 factor the design torque is about 119 N·m, and the coupling's rated torque for the chosen insert must be at least that.
Give the supplier the driver type (electric motor, engine, gearbox), power and speed, driven equipment, both shaft diameters with keyway or spline details, usable shaft lengths, distance between shaft ends, expected angular and parallel misalignment, ambient temperature and contaminants, start/stop or reversing duty, and any space or guarding limits.
02
Lovejoy's spider performance chart gives NBR (Buna-N) rubber spiders −40 to 100 °C with 1° angular and 0.015 in parallel misalignment, high damping and 80A hardness; urethane −34 to 71 °C, 1° and 0.015 in, about 1.5 times the torque of NBR, less damping and not for cyclic or start/stop duty; Hytrel −51 to 121 °C, ½° and 0.015 in, also not for cyclic or start/stop duty; and bronze −40 to 232 °C, ½° and 0.010 in, for speeds up to 250 rpm only. [1]
The catalogue describes jaw couplings as fail-safe — they keep driving if the elastomer fails — and lists variants with radially removable inserts and spacers that let the insert be changed without moving the motor, one limited to 1,750 rpm with its retaining ring. [1] [3]
Linked suppliers list aluminium-alloy single and double diaphragm clamping couplings, clamp and beam couplings for stepper and encoder shafts, and drum gear, diaphragm and tyre couplings for heavy drives. [4] [5]
Editorial note: misalignment figures are limits for the coupling, not installation targets. Align the shafts as closely as practical rather than relying on the limit.
03
Suppliers linked to this page list shaft couplings; each card links to the page reviewed.
The listings reviewed range from small aluminium clamp, beam and diaphragm couplings for servo and stepper axes to cast and forged gear, diaphragm and tyre couplings for rolling mills and heavy drives; ask each for rated and peak torque, maximum speed and misalignment limits per size.
04
This is a functional reference built from the sources cited; it is not one maker's specification.
| Part | Role | Fix in the order |
|---|---|---|
| Hubs | Carry the bores and keyways. [1] [2] | Bores; keyways; material. |
| Flexible element | Spider, disc, diaphragm or tyre; sets torque and misalignment. [1] [4] | Type; material. |
| Clamp or set screw | Fixes hub to shaft. [4] | Clamp or set screw. |
| Spacer | Allows insert change without moving machines. [1] | Spacer length. |
| Gear or grid teeth | Heavy-duty torque transmission. [5] | Type; lubrication. |
| Guard | Covers rotating parts. | Guard. |
05
A shaft coupling quotation needs values for your drive. The table explains each field, gives published values where a reviewed source states them, and says what to obtain from the supplier.
| Field | What it means and published values | Ask the supplier for |
|---|---|---|
| Rated Torque (N·m) | Must cover design torque; example L150 NBR 1,240 in-lb. [1] | Rated and peak torque. |
| Bore Diameter Range (mm) | Jaw range 4.45–178 mm. [3] | Max bore per size. |
| Maximum Speed (rpm) | Example L150 NBR 5,000 rpm; bronze 250 rpm. [1] | Limit per insert. |
| Misalignment Capacity (Angular) (°) | NBR/urethane 1°; Hytrel/bronze ½°. [1] | Angular limit. |
| Misalignment Capacity (Parallel) (mm) | 0.015 in (≈0.38 mm) NBR; 0.010 in bronze. [1] | Parallel limit. |
| Operating Temperature (°C) | NBR −40 to 100; Hytrel −51 to 121. [1] | Range. |
| Torsional Stiffness (kN·m/rad) | Element stiffness. | Value. |
| Material Grade | Hubs: sintered, aluminium, steel, stainless, ductile iron. [3] | Materials. |
| Weight (kg) | Per coupling. | Weight; inertia. |
| Balance Quality Grade | For high-speed couplings. | Grade if needed. |
06
Paste it into your enquiry below or into an email to a maker, then replace every bracket.
Driver: [type; kW; rpm] Driven: [equipment; duty] Shafts: [diameters; keyways; lengths; gap] Misalignment: [angular; parallel expected] Environment: [temperature; oil; dirt] Duty: [start/stop; reversing; shock] Type: [jaw; disc; diaphragm; gear; other] Quantity: [per size]
These companies list shaft couplings.
Lists aluminium-alloy single and double diaphragm clamping and set-screw couplings.
Product scope checked 2026-10-11
Lists flexible gear couplings, diaphragm couplings and cardan shafts.
Product scope checked 2026-10-11
Lists aluminium clamp, rigid and beam shaft couplers for CNC and stepper motor shafts.
Product scope checked 2026-10-11
Lists custom, diaphragm and gear couplings among its castings and forgings.
Product scope checked 2026-10-11
Lists drum gear couplings and universal joint shafts for rolling mills.
Product scope checked 2026-10-11
Lists industrial shaft couplings alongside crane wheels and sheaves.
Product scope checked 2026-10-11
Lists shaft couplings in its mechatronics online store.
Product scope checked 2026-10-11
Lists shaft couplings alongside gears and gearmotors.
Product scope checked 2026-10-11
Lists shaft couplings alongside casters and wheels.
Product scope checked 2026-10-11
Explore company information and manufacturing capabilities, then discuss the scope of your project with a relevant supplier.
Lovejoy uses N·m = kW × 9,550 ÷ rpm, then multiplies by the application service factor to get design torque. [1]
Lovejoy's example uses 1.25 for an electric motor with standard torque driving a rotary pump. [1]
Lovejoy lists 1° angular and 0.015 in parallel for NBR spiders. [1]
Lovejoy says its jaw couplings will still perform if the elastomer spider fails. [3]
Sources checked 2026-10-11. Lovejoy (Timken) is a coupling maker publishing a jaw coupling catalogue with selection method, ratings and insert data, and a selection worksheet; Tianniu and Rokee are linked suppliers.
Ask for use case, specification boundaries, supplier type, and RFQ preparation information for this product.
Compare manufacturer profiles with relevant product and process capability.