Product Overview

The NMT 71901 ACD/HCP4A is an open, single-row super-precision hybrid ceramic angular contact ball bearing. With a 12 mm bore, 24 mm outer diameter, and 6 mm width, this bearing is the ultra-compact member of the 719 series. Featuring a 25° contact angle (ACD type) and D-type high-capacity design, combined with silicon nitride (Si₃N₄) hybrid ceramic rolling elements (HC) and a phenolic resin cage, it integrates high rigidity, high load capacity, ultra-high-speed performance, and super-precision rotational accuracy into a single package, accommodating radial and unidirectional axial loads simultaneously.

 

The bearing offers a radial dynamic load rating of 2.55 kN (574 lbf) and a static load rating of 1.18 kN (266 lbf). Manufactured to the P4A super-precision tolerance class with a 25° contact angle and hybrid ceramic technology, the bearing achieves a limiting speed of 75,000 r/min under grease lubrication and 120,000 r/min under oil-air lubrication. The bearing weighs only 0.01 kg (10 g) with an operating temperature range of -30°C to 110°C.

 

Model Code Decoding – Understanding NMT 71901 ACD/HCP4A

Code Meaning

71901 Basic series designation, 12 mm bore, 24 mm OD, 6 mm width – 719 series ultra-thin design

AC Angular contact design with 25° contact angle – provides higher axial rigidity and axial load capacity compared to 15° designs

D D-type high-capacity design – accommodates heavy loads at relatively high speeds, better suited for heavier loads compared to equivalent B and E type designs

HC Hybrid ceramic – rolling elements made of bearing-grade silicon nitride (Si₃N₄)

P4A Super-precision tolerance class – superior to ABEC 7, bore and OD tolerances -0.004 mm to 0

Core Value: The ACD-type 25° contact angle provides higher axial rigidity and axial load capacity compared to 15° designs – the larger the contact angle, the higher the axial stiffness and axial load capacity. The D-type high-capacity design accommodates heavy loads at relatively high speeds. HC hybrid ceramic technology drastically reduces centrifugal forces and frictional heat at high speeds. P4A super-precision ensures bore and OD tolerances are controlled within -0.004 mm to 0 – these four elements work together to make this bearing the ultimate precision bearing solution for high-rigidity, high-capacity miniature spindles.

 

Core Performance Advantages

1. 25° Contact Angle – High Axial Rigidity and Load Capacity

The 25° contact angle is one of the highest axial rigidity contact angle designs available in angular contact ball bearings. Compared to 15° contact angle (CE type), the ACD-type 25° contact angle provides higher axial rigidity and greater axial load capacity. In applications subjected to heavy axial loads, the 25° contact angle more effectively resists axial displacement, ensuring machining accuracy and spindle stability.

 

2. D-Type High-Capacity Design – High Load in Compact Space

The D-type high-capacity design optimizes ball complement and internal geometry – ball diameter 3.175 mm, 13 ceramic balls per bearing – achieving an outstanding 2.55 kN dynamic and 1.18 kN static load rating within an extremely compact 6 mm width. Compared to equivalent B and E type designs, the D-type design is better suited for heavier loads.

 

3. Hybrid Ceramic Technology – The Foundation of Ultra-High-Speed Performance

Silicon nitride (Si₃N₄) ceramic balls have only 60% the density of bearing steel, drastically reducing centrifugal forces and frictional heat at high speeds. Ceramic materials also offer lower thermal expansion coefficients and higher elastic modulus, effectively suppressing geometric deformation at high speeds while providing excellent electrical insulation and extended service life. Combined with chrome steel rings and a phenolic resin cage, this achieves the perfect balance of high rigidity, ultra-high speed, and durability. The bearing achieves a limiting speed of 75,000 r/min under grease lubrication and 120,000 r/min under oil-air lubrication.

 

4. Extreme Lightweight – Only 10 Grams

The bearing weighs only 0.01 kg (10 g). The extremely low rotating mass effectively reduces centrifugal loads and inertia moments at high speeds.

 

5. P4A Super-Precision Grade – Micron-Level Accuracy

The P4A tolerance class (superior to ABEC 7) guarantees minimal radial runout and axial play. Bore and outside diameter tolerances are -0.004 mm to 0, meeting stringent surface quality and dimensional consistency requirements. Operating temperature range is -30°C to 110°C.

 

6. Lightweight Phenolic Resin Cage

The lightweight high-strength phenolic resin cage provides excellent guidance accuracy and low friction at high speeds, contributing to reduced centrifugal forces, friction, and heat generation – a key factor in achieving the 120,000 r/min oil-air lubrication limiting speed.

 

7. Open Design – Flexible Lubrication Options

This bearing features an open design, allowing flexible selection of lubrication methods based on application – grease lubrication for general ultra-high-speed applications (75,000 r/min), oil-air lubrication for extreme ultra-high-speed machining (120,000 r/min).

 

8. Clear Performance Specifications

 

Parameter Value

Bore d 12 mm

Bore Tolerance -0.004 mm to 0

Outer Diameter D 24 mm

OD Tolerance -0.005 mm to 0

Width B 6 mm

Contact Angle 25°

Dynamic Radial Load 2.55 kN (574 lbf)

Static Radial Load 1.18 kN (266 lbf)

Fatigue Load Limit Pu 0.05 kN (50 N)

Ball Diameter Dw 3.175 mm

Ceramic Balls per Bearing 13

Speed (Grease) 75,000 r/min

Speed (Oil-Air) 120,000 r/min

Ball Material Silicon Nitride (Si₃N₄)

Ring Material Chrome Steel

Cage Material Phenolic Resin

Seal Type Open

Tolerance Class P4A (ABEC 7)

Arrangement Non-Universal Matchable

Weight 0.01 kg (10 g)

Temperature Range -30°C to 110°C

Typical Applications

The NMT 71901 ACD/HCP4A, with its 25° contact angle high axial rigidity, D-type high-capacity design, and P4A super-precision grade, covers an exceptionally wide range of high-end miniature applications:

 

High-Speed Machine Tool Spindles – precision micro-machining centers, CNC engraving/milling spindles

 

Precision Grinding Machines – high-accuracy internal/external grinding, jig grinder spindles

 

High-Frequency Motors – high-speed, high-precision miniature motors

 

Dental Handpieces – high-speed dental turbine handpieces

 

Aerospace Components – gyroscopes, actuators, jet engine parts

 

Semiconductor Manufacturing Equipment – precision wafer dicing, chip packaging spindles

 

Medical Surgical Power Tools – high-speed orthopedic drills, micro-surgical instruments

 

Industrial Robots – micro high-speed rotary joints

 

Food Machinery, Indexing Heads, Coating Equipment and other industrial precision equipment

 

Important Installation Notes

✅ This is a single-row open design bearing – select appropriate lubrication method based on application: grease lubrication for general ultra-high-speed applications (limiting speed 75,000 r/min), oil-air lubrication for extreme ultra-high-speed machining (limiting speed 120,000 r/min).

 

✅ This is a non-universal matchable single bearing (no G/GA suffix). For paired configurations (DB, DF, DT arrangements), please order the corresponding pre-matched set.

 

⚠️ Ensure shaft and housing fits comply with P4A grade requirements (bore tolerance -0.004 mm to 0, OD tolerance -0.005 mm to 0) to achieve the expected rotational accuracy and service life.

 

⚠️ A single-row angular contact ball bearing can accommodate axial load in one direction only. Radial loads generate an additional axial force that must be counteracted through paired mounting.

 

⚠️ This bearing has no preload setting – preload must be adjusted during paired installation based on the specific configuration.

 

⚠️ Hybrid ceramic bearings are more sensitive to installation shock. Heat mounting or hydraulic installation methods are recommended – avoid impact on raceways or rolling elements. Due to the extremely small size (only 10 g), extra care is required during installation to avoid excessive force.

 

✅ Installation in a clean environment is recommended to prevent contaminant ingress that could affect ultra-high-speed performance.

 

NMT Quality Commitment

Japan NMT (Enmutī) applies strict Japanese quality standards to every 71901 ACD/HCP4A bearing – from ring material (high-purity chrome steel), ceramic balls (HIP silicon nitride), to superfinishing processes. The combination of 25° contact angle (ACD type), D-type high-capacity design, hybrid ceramic technology (HC), P4A super-precision, and phenolic resin cage makes this bearing the flagship miniature precision bearing in the NMT 719 series – offering the perfect balance of high axial rigidity, high load capacity, and ultra-high-speed performance.

 

Choose NMT 71901 ACD/HCP4A for:

 

✅ 25° contact angle – high axial rigidity and load capacity

 

✅ D-type high-capacity design – 2.55 kN high load capacity

 

✅ Hybrid ceramic technology – 120,000 r/min ultra-high-speed performance

 

✅ Extreme lightweight – only 10 g

 

✅ P4A super-precision running accuracy – bore/OD tolerance -0.004 mm to 0

 

✅ Lightweight phenolic resin cage – low friction, low noise, high speed

 

✅ Steel rings + ceramic balls – high rigidity, ultra-high speed, cost-effectiveness

 

✅ Open design – flexible lubrication options