Roller Chain Sprockets | A-Plate & B-Hub – 18 to 72 Teeth, SAE 1045 Steel

Single Strand Roller Chain Sprockets

Korea Ever-Power #25 roller chain sprockets cover A-plate (18–72 teeth, outside diameter 1.568″–5.876″) and B-hub (10–72 teeth) configurations in SAE 1045 steel with precision-cut teeth and black oxide finish. At just 0.03–1.30 lb per unit, these are the lightest sprockets in the ANSI range — ideal for small-format drive systems in instrumentation, light conveyor chain applications, medical equipment, and precision machinery across Korea.

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#25 Chain Sprockets — ANSI Light-Duty Series, A-Plate and B-Hub

#25 roller chain is the smallest ANSI standard chain size, with a pitch of 1/4 inch (6.35 mm) and a breaking strength of approximately 780 lbf (354 kgf). The corresponding #25 sprockets are designed for drives where the transmitted power is low but precision and smooth engagement matter — think instrument panel drives, vending machine mechanisms, seed counting equipment, and light packaging machinery. The 1/4-inch pitch means a high tooth count can be achieved in a very compact outside diameter, which is why #25 drives are often found in space-constrained control mechanisms.

Six Standard Hub Configurations

Korea Ever-Power manufactures #25 sprockets in two hub configurations. A-plate sprockets (25A series, 18–72 teeth) are flat discs with no hub — minimal axial thickness, suitable for flush-mount or weld-on installations. B-hub sprockets (25B series, 10–72 teeth) carry a single-sided hub that extends shaft engagement length and accepts a keyway plus set screws for reliable torque transmission. Both types are SAE 1045 steel with black oxide finish as standard.

  • ⚙Chain: ANSI #25 — pitch 1/4″ (6.35 mm), roller dia 0.130″, inner width 0.125″
  • ⚙A-plate range: 18–72 teeth, OD 1.568″–5.876″, weight 0.04–0.74 lb
  • ⚙B-hub range: 10–72 teeth, OD 0.919″–5.876″, weight 0.03–1.30 lb
  • ⚙Material: SAE 1045 steel, black oxide finish, ANSI B29.1 compliant

#25 A-Plate Sprocket Specifications

A-plate (#25A) sprockets have no hub projection — the bore passes directly through the flat plate body. The stock bore listed is the minimum standard bore; larger bores up to the outside diameter constraint can be machined on request. Outside diameter values below are nominal imperial measurements per ANSI B29.1.

Sprocket Size Teeth Type Outside Dia. Stock Bore Weight (lb)
25A18 18 A 1.568″ 1/4″ 0.04
25A19 19 A 1.648″ 1/4″ 0.04
25A20 20 A 1.729″ 1/4″ 0.04
25A21 21 A 1.809″ 3/8″ 0.04
25A22 22 A 1.889″ 3/8″ 0.06
25A23 23 A 1.969″ 3/8″ 0.06
25A24 24 A 2.049″ 3/8″ 0.08
25A25 25 A 2.129″ 3/8″ 0.08
25A26 26 A 2.209″ 3/8″ 0.09
25A28 28 A 2.369″ 3/8″ 0.11
25A30 30 A 2.529″ 3/8″ 0.13
25A36 36 A 2.972″ 3/8″ 0.15
25A42 42 A 3.454″ 1/2″ 0.19
25A48 48 A 3.937″ 1/2″ 0.24
25A54 54 A 4.442″ 1/2″ 0.38
25A60 60 A 4.920″ 1/2″ 0.54
25A72 72 A 5.876″ 1/2″ 0.74

#25 B-Hub Sprocket Specifications

B-hub (#25B) sprockets carry a single hub projection on one face, providing a longer bore engagement length for keyway-and-set-screw shaft retention. The "Recommend Max. Bore" column is the largest bore that can be machined while maintaining adequate hub wall thickness. "Length Thru Bore" is the overall axial hub engagement depth — a critical value when sizing a key length or checking shaft protrusion clearance.

Size Teeth OD Stock Bore Max Bore Hub Dia. Length Thru Bore Weight (lb)
25B10 10 0.919″ 1/4″ 1/4″ 1/2″ 1/2″ 0.03
25B11 11 1.002″ 1/4″ 5/16″ 9/16″ 1/2″ 0.04
25B12 12 1.083″ 1/4″ 3/8″ 5/8″ 1/2″ 0.06
25B13 13 1.167″ 1/4″ 7/16″ 23/32″ 1/2″ 0.07
25B14 14 1.248″ 1/4″ 1/2″ 3/4″ 1/2″ 0.08
25B15 15 1.330″ 1/4″ 5/8″ 7/8″ 5/8″ 0.09
25B16 16 1.410″ 1/4″ 5/8″ 7/8″ 5/8″ 0.10
25B17 17 1.492″ 1/4″ 5/8″ 7/8″ 5/8″ 0.12
25B18 18 1.568″ 1/4″ 3/4″ 1″ 5/8″ 0.13
25B20 20 1.729″ 1/4″ 3/4″ 1″ 5/8″ 0.14
25B21 21 1.809″ 3/8″ 3/4″ 1-1/8″ 5/8″ 0.15
25B24 24 2.049″ 3/8″ 3/4″ 1-1/8″ 5/8″ 0.18
25B30 30 2.529″ 3/8″ 3/4″ 1-1/8″ 3/4″ 0.27
25B36 36 2.972″ 3/8″ 3/4″ 1-1/8″ 3/4″ 0.37
25B42 42 3.454″ 1/2″ 3/4″ 1-1/8″ 3/4″ 0.49
25B48 48 3.937″ 1/2″ 1-3/8″ 2″ 3/4″ 0.75
25B54 54 4.442″ 1/2″ 1-3/8″ 2″ 3/4″ 0.90
25B60 60 4.920″ 1/2″ 1-3/8″ 2″ 3/4″ 1.10
25B70 70 5.717″ 1/2″ 1-3/8″ 2″ 3/4″ 1.25
25B72 72 5.876″ 1/2″ 1-3/8″ 2″ 3/4″ 1.30

#25 roller chain pitch 6.35mm components definition

SAE 1045 vs. SAE 1018 Steel — Why the Material Grade Matters

Many #25 sprockets in the market are made from SAE 1018 low-carbon steel — the industry baseline. Korea Ever-Power specifies SAE 1045 medium-carbon steel for all sprockets. The difference is not marketing language — it has measurable consequences for how long the sprocket lasts in service.

Property SAE 1045 (Korea Ever-Power) SAE 1018 (Common Baseline)
Carbon content 0.43–0.50% 0.15–0.20%
Tensile strength 570–700 MPa 400–490 MPa
Surface hardness (normalised) 163–207 HB 126–163 HB
Induction hardenability Excellent — achieves 50–58 HRC surface Poor — insufficient carbon for deep hardening
Tooth wear resistance Significantly higher — especially on small sprockets Adequate for very low-speed, low-load applications only
Machinability Good — suitable for custom bore machining Very good — easier to machine, but at cost of strength

For #25 sprockets specifically, the higher tensile strength of SAE 1045 matters because the small pitch means each tooth carries load over a short engagement arc. Higher tooth-face hardness (achieved through induction hardening on sub-30-tooth sprockets) directly extends the period before tooth-face wear requires sprocket replacement.

Characteristics of #25 Chain Drive Systems

#25 roller chain sprocket engagement animation small pitch drive

#25 is the lightest and most compact ANSI roller chain size, and this brings specific design characteristics that engineers working with #25 drives should understand before specifying sprockets:

📐 Compact Pitch = Higher Tooth Count in Small Diameter

A 36-tooth #25 sprocket has an outside diameter of just 2.972″ (75.5 mm). To achieve the same pitch circle with an #80 chain (a common mid-range size), you would need a 9-tooth sprocket — which is below the recommended minimum. This compact-to-tooth-count ratio makes #25 ideal for high gear-ratio drives in small enclosures, where a 4:1 or 5:1 ratio can be achieved with sprockets that fit inside a standard equipment panel.

⚡ Speed Limits and Polygon Effect

#25 chain can run at higher shaft speeds than larger chains before noise and wear become problematic — because the small pitch means a higher number of tooth engagements per unit length, which smooths out the polygon effect. Practical speed limits for #25 drives are approximately 1,500–2,000 rpm on a 17-tooth sprocket, which equates to a chain speed of around 7–9 m/s. Above this, vibration and noise increase rapidly and a timing belt or gear drive should be considered instead.

🔧 Lubrication and Maintenance

#25 chain is more sensitive to inadequate lubrication than heavier chains because the small pin and bushing diameters leave little tolerance for additional wear before the chain pitch elongates beyond the replacement threshold. Apply a light penetrating chain lubricant every 200–400 hours for drives operating at moderate speeds. In dusty environments, keep sprockets clean — abrasive particles embedded between roller and sprocket tooth are the primary cause of accelerated wear on small-pitch drives.

Typical Applications for #25 Chain and Sprockets

🔬 Instruments and Scientific Equipment

#25 sprocket scientific instrument laboratory equipment

Analytical instruments, laboratory automation equipment, and medical diagnostic devices frequently use #25 chain drives for sample transport mechanisms, reagent positioning stages, and dosing pump drives. The compact size and low weight per unit length (approximately 0.08 kg/m for #25 standard) make it the practical choice where mechanical noise and vibration must be minimised and the load is below 1 kW.

🏭 Packaging and Vending Machinery

#25 sprocket packaging vending machine mechanism

Vending machines, packaging equipment, and food dispensing systems across Korea use #25 chain extensively for product transport belts, elevator mechanisms, and portion-control drives. The B-hub 25B14 to 25B24 range covers most vending mechanism drive requirements. The black oxide finish provides adequate corrosion resistance for temperature-controlled indoor environments where these machines typically operate.

🌾 Seed Metering and Precision Agriculture

#25 sprocket seed drill metering agricultural precision

Precision seed drills and transplanting machines use #25 chain for final drive to seed metering discs where fine tooth-count increments allow precise seeding rate adjustment. A-plate sprockets in the 25A30–25A54 range are typical for this application — the flat profile allows multiple sprockets to be stacked side-by-side on the same shaft for different seed spacing selections.

Compatible #25 Roller Chain

#25 ANSI roller chain light duty 1/4 inch pitch

All #25 sprockets listed above are dimensioned for use with ANSI #25 roller chain — pitch 0.250″ (6.35 mm), roller diameter 0.130″, inner width 0.125″. Korea Ever-Power stocks #25 chain in single-strand, double-strand (#25-2), and connecting links to pair with the sprockets above. When ordering a matched set, specify the tooth counts for both driver and driven sprocket plus your shaft centre distance, and we will calculate the required chain link count.

For broader chain and sprocket system guidance covering power rating selection, centre distance calculations, and lubrication recommendations for #25 drives, our technical team can assist before your order is placed.

Why Korea Ever-Power Chain and Sprocket

Korea Ever-Power sprocket manufacturing workshop #25 chain sprocket

Korea Ever-Power Chain and Sprocket Co., Ltd. stocks the complete #25 A-plate and B-hub range with fast Korea dispatch:

✦SAE 1045 steel as standard — not the 1018 baseline used by many suppliers; measurably higher tensile strength and hardenability
✦Induction-hardened teeth on all sprockets with fewer than 30 teeth — reduced wear rate on the most-stressed small sprockets
✦Full A-plate and B-hub range in stock — 18–72T A-plate and 10–72T B-hub, all standard sizes available without special-order lead time
✦Custom bore machining — keyways and set screw tappings to drawing; 5–10 day turnaround for custom bore orders
✦ANSI B29.1 pitch diameter verified — dimensional inspection on each production batch before dispatch
✦7–14 day Korea delivery — no import wait; matched #25 chain available from the same stock location

Frequently Asked Questions

What is the difference between #25 and #35 chain — can I use a #25 sprocket with #35 chain?
#25 and #35 are both ANSI standard chains but with different pitches — #25 has a 1/4-inch pitch (6.35 mm) and #35 has a 3/8-inch pitch (9.525 mm). They are not interchangeable. A #25 sprocket will not mesh correctly with #35 chain. Always match the sprocket chain number to the chain markings exactly. The chain number stamped on the outer plate or connecting link is the definitive reference.
Why does the B-hub series start at 10 teeth but A-plate starts at 18 teeth?
Small tooth counts (10–17) require a hub for adequate shaft engagement because the sprocket outside diameter at these tooth counts is too small to have a usable bore through a flat plate alone — the wall thickness between bore and tooth root would be insufficient for a key. The B-hub provides the necessary engagement length by extending the bore into the hub projection. From 18 teeth upward, the plate body is large enough in diameter to support a flat-plate bore with adequate wall thickness.
What is the maximum shaft diameter for a 25B18 sprocket?
The 25B18 has a recommended maximum bore of 3/4″. This is the largest bore that can be machined while leaving a hub wall thick enough for a standard set screw and key. The stock bore supplied is 1/4″ — any bore between 1/4″ and 3/4″ can be machined to your exact shaft dimension. Specify the required bore diameter, keyway width and depth, and whether you need one or two set screws when ordering a custom-bore sprocket.
Can #25 sprockets run stainless steel chain?
Yes. #25 stainless steel roller chain has the same pitch (1/4 inch), roller diameter, and inner width as standard #25 chain — so #25 steel sprockets mesh with stainless chain without any dimensional modification. However, if the application requires corrosion resistance throughout the drive (e.g., food processing wash-down environments), specify our stainless steel #25 sprockets to match. Running stainless chain on carbon steel sprockets creates a galvanic and chemical environment that can accelerate tooth corrosion on the sprocket side over time in wet conditions.
How do I prevent #25 chain from jumping off the sprocket during reversing operation?
Chain derailment during reversal is usually caused by too much slack in the chain at the moment of direction change. For any drive that reverses frequently: keep chain sag below 2% of centre distance rather than the standard 2–4%; use a chain tensioner on the slack run; and increase the minimum tooth count to at least 17 on the smaller sprocket. A sprocket with fewer than 15 teeth on a reversing drive will experience significant wrap-angle loss on each reversal, which combined with chain inertia is the primary cause of derailment.
What is the recommended centre distance for a #25 chain drive?
ANSI B29.1 recommends a centre distance of 30–50 times the chain pitch. For #25 chain (6.35 mm pitch) this gives an ideal centre distance range of approximately 190–320 mm. Below 30 pitches, the wrap angle on the smaller sprocket becomes too small for reliable engagement. Above 50 pitches, chain vibration and the difficulty of maintaining correct tension increase. For very short centre distances (under 30 pitches), a larger chain size with fewer teeth on each sprocket is usually a better solution.

Customer Reviews

Verified feedback from customers in Korea and surrounding markets.

Lee Jae-won, R&D Engineer, Medical Device Company, Seongnam (early 2025)

"We use #25 chain drives in a sample transport mechanism inside a diagnostic instrument. Precision and low noise are non-negotiable. Korea Ever-Power 25B18 and 25B30 sprockets have been running in our prototype for six months without measurable pitch diameter wear. The custom bore machining (8mm diameter, 3mm key) was accurate to within our drawing tolerance of ±0.02mm."

Kwon Min-seo, Mechanical Engineer, Vending Machine Manufacturer, Gyeonggi-do (2024)

"We buy #25 B-hub sprockets in 14T, 18T, and 24T for our vending machine product elevator mechanisms. Korea Ever-Power stock these in the correct bore sizes and lead time is consistently 9–11 days. We have been sourcing from them for about 14 months and have had zero dimensional non-conformances on arrival inspection."

Ahn Soo-ji, Production Engineer, Agricultural Equipment OEM, Chungbuk (Q4 2024)

"For seed drill metering drives we need multiple tooth count options in A-plate to adjust seeding rates without changing the chain. We use 25A30, 25A36, 25A42, and 25A48. Korea Ever-Power supplies all four in a single order. The flat plate profile stacks cleanly on our metering shaft with minimal spacing, which is exactly what our design requires."

Park Ji-ho, Maintenance Technician, Electronics Assembly Plant, Incheon (2025)

"We maintain #25 chain drives on component transport trays in our PCB assembly line. The SAE 1045 sprockets from Korea Ever-Power last noticeably longer than the 1018-based sprockets we used previously from a domestic supplier. Specifically the 25B12 and 25B15 — the small teeth used to show wear after about 4 months. With Ever-Power we are now at 9 months on the current set without tooth-face wear reaching the replacement threshold."

Oh Sung-min, Design Engineer, Printing Equipment Company, Seoul (early 2025)

"#25 A-plate sprockets for auxiliary register drives on our sheet-fed press. We needed 25A20 and 25A30 with a 6mm bore, which is non-standard. Korea Ever-Power machined the custom bore with a 2mm key slot exactly to our drawing. The response time from drawing submission to delivery confirmation was four business days."

 

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