Ball Bearing Idler Sprockets European Standard | Free-Running Tensioner Sprockets DIN 8187

idler-sprocket-1

Pre-assembled ball bearing idler sprockets to DIN 8187 / ISO R606. Sealed bearing, free-running on fixed pin. Chain sizes 5mm pitch to 31.75mm pitch. For chain tensioning, slack-strand support and chain guide applications. Korea Ever-Power factory-direct.

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9 Sizes

Pitch Range Available

Sealed 2RS

Bearing Type

Ø16–25 mm

Pin Bore Range

ISO 9001

Certified Quality

Ball Bearing Idler Sprockets – Product Overview

Ball bearing idler sprockets are non-driven chain sprockets that rotate freely on a fixed pin or shaft. Unlike drive sprockets — which are keyed or bushed to a rotating shaft — idler sprockets have a sealed deep-groove ball bearing pressed into the hub bore, allowing the sprocket to spin freely around a stationary mounting pin. This makes them the correct component for chain tensioning, slack-strand support and chain direction-change applications where no power transmission through the sprocket is required.

Korea Ever-Power idler sprockets are supplied as a complete ready-to-mount assembly — the ball bearing is already pressed into the sprocket hub and pre-packed with lithium grease. The 2RS double-lip rubber seal on both faces of the bearing prevents ingress of chain oil, dust and moisture into the bearing race, making the assembly suitable for use in dusty agricultural and industrial environments without any additional lubrication or sealing work at installation. Every assembly is test-spun before despatch to confirm free rotation and correct bearing seating.

The tooth profile of every idler sprocket conforms to DIN 8187 / ISO R606 — full compatibility with any European standard roller chain of the matching pitch. The idler engages the chain in the same geometry as a drive sprocket, distributing the contact load correctly across the tooth root radius and avoiding the accelerated wear that results from mismatched tooth profiles on tensioner sprockets.

Also available in this series: disassembling hubs for platewheels — solid-disc flanged hubs with a central bore and bolt flange, used to build custom platewheel idler assemblies for flat-top and attachment chain. Hub sizes dm=30 mm to dm=160 mm. See the full sprocket category for all available types and configurations.

Korea Ever-Power ball bearing idler sprocket free-running tensioner DIN 8187

📍 Where idler sprockets are used

  • Tensioner sprocket — maintains chain tension on the slack strand to prevent chain jump
  • Take-up sprocket — adjustable idler on a sliding carriage for chain elongation compensation
  • Guide sprocket — changes chain direction around an obstacle without a driven shaft
  • Anti-sag support — prevents long chain spans from drooping under their own weight

Idler Sprocket vs Drive Sprocket — Key Differences

Using the wrong sprocket type in a tensioner position is a common installation error. An idler sprocket is not simply a "spare" drive sprocket — the two are designed differently for fundamentally different load conditions.

Feature Ball Bearing Idler Standard Drive Sprocket
Mounting Fixed pin — sprocket rotates around stationary pin Rotating shaft — sprocket turns with shaft
Bearing Deep-groove ball bearing 2RS, pre-packed, sealed No bearing — bore takes key and setscrew
Power transmitted None — guides and tensions chain only Full rated chain drive power
Lubrication required None — sealed bearing maintenance-free Chain lubrication as normal
Replacement trigger Bearing noise, rough rotation or tooth wear Tooth wear or pitch circle elongation
Can drive sprocket replace idler? ❌ No — a drive sprocket on a fixed pin has no bearing and will seize immediately

Column key: Z = tooth count  |  Pitch = chain pitch (in") × inner width (in")  |  de = tip diameter (mm)  |  dp = pitch circle diameter (mm)  |  A = tooth width (mm)  |  D1 = bore for pin/shaft (mm)  |  F = bearing flange OD (mm)  |  B = assembly width (mm)  |  H = bearing seat depth (mm)

Ball Bearing Idler Sprocket Specifications

All assemblies supplied complete with 2RS sealed ball bearing pre-installed. DIN 8187 / ISO R606 tooth profile. Pin bore D1 = bore for stationary mounting pin.

Z Chain Pitch ISO Chain de (mm) dp (mm) A (mm) D1 Pin Bore (mm) F (mm) B (mm) H (mm)
Light-pitch idlers — 5 mm to 9.525 mm pitch
23 3/8″ × 7/32″ — 62.15 58.75 2.8 16 40 12 18.3
21 3/8″ × 7/32″ 06B-1 68.0 63.90 5.3 16 40 12 18.3
08B / 1/2″ pitch idlers — 12.70 mm pitch
16 1/2″ × 5/16″ 08B-1 69.5 65.10 7.2 16 40 12 18.3
18 1/2″ × 5/16″ 08B-1 77.8 73.14 7.2 16 40 12 18.3
10B / 5/8″ pitch idlers — 15.875 mm pitch
14 5/8″ × 3/8″ 10B-1 78.0 71.34 9.1 16 40 12 18.3
17 5/8″ × 3/8″ 10B-1 93.0 86.39 9.1 16 40 12 18.3
12B / 3/4″ pitch idlers — 19.05 mm pitch
13 3/4″ × 7/16″ 12B-1 87.5 79.59 11.1 16 40 12 18.3
15 3/4″ × 7/16″ 12B-1 99.8 91.63 11.1 16 40 12 18.3
16B / 1″ pitch idlers — 25.40 mm pitch
12 1″ × 17.02 mm 16B-1 109.0 98.14 16.2 20 47 14 17.7
20B / 1¼″ pitch idlers — 31.75 mm pitch
13 1¼″ × 3/4″ 20B-1 147.8 132.65 18.5 25 52 15 21.0

All assemblies include 2RS sealed bearing pre-installed and pre-packed with lithium grease. Pin bore D1 tolerance: H7. Non-catalogue tooth counts and custom pin bores available — contact us with specification.

Chain Tensioner Design — Best Practice

Correct tensioner positioning and idler sprocket selection prevents the three most common chain drive failures: chain jump, chain fatigue cracking and roller impact wear.

Position on the Slack Strand

The tensioner idler must always be placed on the slack (return) strand — the side of the chain drive that is not pulling. Placing a tensioner on the tight strand increases the load on the drive sprocket, the shaft bearings and the chain itself without providing any tensioning benefit. For a horizontal drive, the slack strand is typically the lower run; for a vertical drive, it is usually the returning side opposite the direction of rotation.

Minimum Wrap Angle — 120°

The chain must wrap at least 120° around the drive sprocket for reliable power transmission without chain jump. If the natural wrap angle from geometry is below 120°, an idler sprocket on the slack strand near the drive sprocket can increase wrap angle. Move the idler inward (toward the chain run) to increase the wrap — each 10 mm of inward movement increases wrap angle by approximately 2° for typical drive proportions.

Idler Tooth Count — Minimum 17T

Use the same minimum tooth count guideline for the idler sprocket as for a drive sprocket — 17 teeth minimum for smooth engagement at normal conveyor speeds. Below 17T the polygon effect becomes noticeable as a rhythmic load variation in the chain each time a roller seats on the sprocket — on an idler this is less critical than on a drive sprocket, but it still contributes to chain fatigue over time on high-cycle applications.

Spring vs Fixed Tensioner

A fixed idler (mounted in a fixed position) compensates for the initial chain installation sag but cannot accommodate chain elongation over service life. A spring-loaded idler maintains constant tension as the chain elongates. For drives on agricultural machinery and conveyors with frequent start-stop cycling, a spring-loaded idler using a ball bearing idler sprocket on a pivot arm is best practice — it absorbs the inertia shock on start-up and maintains tension as the chain wears.

Applications

Agricultural Machinery Tensioners

Combine harvester, baler and header chain tensioning is among the most demanding idler applications — the chain experiences cyclic tension variation as the threshing drum loads and unloads. Ball bearing idler sprockets on spring-loaded pivot arms absorb this tension variation while maintaining minimum chain sag. The 10B-1 and 12B-1 idlers (Z=14–17) are most commonly specified in combine and baler drives.

Conveyor Take-Up Systems

Gravity or screw take-up units on industrial conveyors use idler sprockets on a sliding carriage to compensate for chain elongation. As the chain wears and elongates, the carriage moves to maintain tension. Ball bearing idler sprockets are essential here — a plain bore sprocket on a fixed pin would seize without lubrication. See the full sprocket range for drive sprockets to pair with these idlers.

Packaging & Food Processing Lines

High-speed packaging machine chain drives use idler sprockets to maintain chain tension at constant speed — the 06B-1 and 08B-1 idlers at Z=16–21 are the typical specification. The sealed 2RS bearing requires no regreasing during normal service life, which is important in food plant environments where lubricant contamination of product must be prevented.


Korea Ever-Power ball bearing idler sprocket quality inspection and test rotation

Technical Features

2RS Sealed Bearing — Maintenance-Free

The 2RS double-lip rubber seal creates a positive barrier on both bearing faces. The suffix "2RS" (two rubber seals) designates a sealed bearing factory-greased for life — no grease nipple, no regreasing interval. The seal lip contacts the inner ring with a small interference, preventing the entry of dust, water and chain oil while retaining the factory grease charge for the bearing's service life (typically 5,000–10,000 hours at normal idler loads).

Pre-Assembled — Test-Spun Before Despatch

Every idler sprocket assembly is test-rotated after assembly to confirm free rotation, correct bearing seating and no binding. An idler sprocket that binds — either through an incorrectly pressed bearing or a tolerance mismatch — will cause localised chain wear at the contact point rather than smooth rolling contact. The pre-despatch spin test eliminates this risk before the assembly reaches the customer.

DIN 8187 Tooth Profile

Identical tooth geometry to the drive sprocket range. A mismatched idler tooth profile — common when a non-standard tensioner sprocket is substituted — causes the chain roller to seat at the wrong radius on the tooth, concentrating load at the root or tip rather than distributing it across the tooth face. This accelerates wear on both the idler and the chain rollers. Use a DIN 8187 idler with matched European standard roller chain for correct engagement.

Disassembling Platewheel Hubs

In addition to the standard idler sprocket range, this series includes disassembling flanged hubs for platewheel idlers — solid disc hubs with a central bore (dm=30 to dm=160 mm) and bolt-on flange, allowing flat-top chain and attachment chain to pass over the idler without catching on tooth recesses. The hub diameter di ranges from 45 mm (Nr.30 hub) to 205 mm (Nr.160 hub). Used in slat conveyor return-strand idler positions.

Matching Chain & Related Products

European standard roller chain DIN 8187 for ball bearing idler sprockets

Matching Drive Chain — European DIN 8187

Match your idler sprocket with the correct European standard roller chain in DIN 8187 / ISO R606 — the same pitch and strand count as the drive. Standard, heavy-duty H-series and self-lubricating variants available for all sizes.

View Chain Range →

Korea Ever-Power driving chains A and B series

Driving Chains

A and B series short pitch precision roller chains for power transmission. Pitch 9.525 mm to 76.2 mm, simplex to triplex.

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Leaf Chains

BL and LH series hoisting chains for forklift masts and industrial hoist mechanisms. Breaking loads from 11 kN to 1,600+ kN.

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Korea Ever-Power stainless steel chains for food and pharma

Stainless Steel Chains

SUS304 and SUS316L roller chains for food, pharmaceutical, and chemical washdown environments.

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Korea Ever-Power engineering chains for heavy industry

Engineering Chains

Welded steel, cast, and forged chains for cement, steel, mining, and chemical plant heavy conveying.

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Frequently Asked Questions

Can I use a standard drive sprocket as an idler by mounting it on a fixed pin?
No. A standard drive sprocket has a plain bore — when mounted on a fixed pin, the bore slides against the stationary pin with no bearing and no lubrication. Under chain load the sprocket presses against the pin with significant radial force. Without a bearing, the bore will seize onto the pin within minutes of running under load, causing either the sprocket or pin to be destroyed. An idler sprocket must have a ball bearing or similar rolling element bearing between the pin and the sprocket hub — this is the entire purpose of the idler sprocket assembly design.
What pin material and diameter should I use with the idler sprocket?
The pin bore D1 (16 mm for most sizes, 20 mm for 16B idler, 25 mm for 20B idler) must be matched with a ground steel pin of the corresponding diameter machined to h6 or h7 tolerance — a sliding fit in the bearing bore. The pin material should be medium carbon steel (C45 or 42CrMo) with a surface hardness of 55–62 HRC at the bearing contact surface to prevent fretting of the pin under the oscillating bearing load. Through-hardened pins in the correct diameter are available from Korea Ever-Power as an accessory — specify when ordering the idler assembly.
How do I know when an idler sprocket bearing needs replacing?
Three reliable indicators: (1) Audible bearing noise — a grinding, clicking or rumbling sound from the idler position that is not present from the drive sprockets. Spin the idler by hand with the chain removed — a healthy bearing feels smooth with no perceptible roughness. (2) Axial play — wiggle the sprocket axially on the pin. A worn bearing shows noticeable axial movement (more than 0.3 mm). (3) Elevated temperature — an idler sprocket running hotter than the surrounding chain or drive sprocket indicates a failing bearing with increased rolling resistance. Replace the complete assembly — pressing a new bearing into a worn or scored hub is not recommended as hub concentricity cannot be guaranteed after the original bearing has failed.
What are the disassembling platewheel hubs used for?
Disassembling hubs (solid disc platewheel hubs with bolt-on flanges, sizes dm=30 to dm=160 mm) are used to construct custom idler platewheel assemblies for flat-top chain and attachment chain. The solid disc face — with no tooth recesses — prevents the extended attachment plates or slat brackets of the chain from catching in sprocket tooth spaces as the chain passes over the idler. A ball bearing or plain bearing is pressed into the central bore of the hub. These are used in slat conveyor return-strand idler positions, elevator return-strand positions and anywhere attachment chain must pass over a non-driven sprocket position without snagging. The hub disassembles (hence the name) to allow the bearing to be replaced without destroying the hub.

What Our Customers Say

★★★★★

"We fit Korea Ever-Power 10B-1 ball bearing idler sprockets on the spring-tension arms of our baler chain drive system. Previously we were replacing idler assemblies every season — the plain-bore substitute we were using would seize within 200 hours. The sealed bearing assembly from Korea Ever-Power ran the full 1,200-hour season without any maintenance. Night and day difference."

J.O., Farm Machinery Service
France – Agricultural Machinery

★★★★★

"We supply conveyor components across the UK food processing industry. The Korea Ever-Power 08B-1 idler sprockets are our standard specification for all new conveyor builds. The 2RS seal keeps chain lubrication out of the bearing — important in food environments where contamination must be minimised. We stock 06B, 08B and 10B idlers from this range permanently."

T.R., Technical Sales Director
United Kingdom – Conveyor Components Distributor

★★★★★

"We design packaging machines using 06B-1 chain at 2.5 m/s. The tensioner position requires a free-running idler. Korea Ever-Power 06B-1 ball bearing idler at Z=21 fits our standard 16 mm tensioner pin exactly. We have tested 8,000 hours in production without bearing failure. The pre-spin test gives us confidence the assembly is correct before installation."

E.K., Design Engineer
Germany – Packaging Machinery OEM

Request a Quote for Ball Bearing Idler Sprockets

Specify chain size (e.g. 10B-1), tooth count and pin bore diameter. Complete assembly with 2RS bearing supplied. Quantities from 1 piece. Response within one working day.

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