68/2.5 is an Open Miniature Ball Bearing, 68/2.5 Bearing has an inner diameter of 2.5mm, 68/2.5 small Bearing outer diameter is 6mm and 68/2.5 Bearing width is 1.8mm, 68/2.5 Bearing is made of Chrome Steel, 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: 68/2.5 Bearing
• Type: Radial Miniature Bearing
• Closures: Open
• 68/2.5 Dimensions: 2.5mm x 6mm x 1.8mm
• Size: 2.5 x 6 x 1.8 mm
• Standard: Metric
• Bearing Inner Diameter: 2.5mm
• Bearing Outer Diameter: 6mm
• Bearing Width: 1.8mm
• Material: 52100 Chrome Steel
• Quality: Standard Precision
• Quantity: One Bearing