L-940 is an Open Miniature Ball Bearing, L-940 Bearing has an inner diameter of 4mm, L-940 small Bearing outer diameter is 9mm and L-940 Bearing width is 2.5mm, metric 4x9x2.5 mm, L-940 Bearing is made of Chrome Steel grade 52100, 52100 is a high carbon, chromium containing low alloy steel, heat treatment and hardening of 52100 alloy steels will get you 60 Rockwell hardness and very common in bearings.

• Item: L-940 Bearing
• Design Type: Single row deep groove ball bearings
• L-940 Bearing Inner Diameter: 4mm
• L-940 Bearing Outer Diameter: 9mm
• L-940 Bearing Width: 2.5mm
• Size: 4 x 9 x 2.5 mm
• Size Type: Miniature Bearing
• Closures: Open
• Material: 52100 Chrome Steel
• L-940 Dimensions: 4mm x 9mm x 2.5mm
• Standard: Metric
• Load Type: Radial Bearing and can take minimal axial loads
• Quality: Standard Precision
• Quantity: One Bearing

L-940 is categorized as a miniature deep groove ball bearing, and have single row of steel balls that has a deep groove raceway that enables the bearings to take radial loads and axial loads in both directions. L-940 is commonly used in high speed applications, and of course they are designed to be mounted on rods (round shafts).