Closed with metal guards to protect the bearing from dust or any possible contamination. Generally used for electric motors, wheel bearings, agriculture, transportation and many more. Product Name: Deep Groove Ball Bearing; Model Number: 686Z Inner Diameter: 6mm / 0.24 inch; Outer Diameter: 13mm / 0.51 inch Height: 5mm / 0.2 inch; Color: Silver Tone Material: Metal Net Weight: 140g Package Contents: 50 x Deep Groove Ball Bearings Only the above package content, other products are not included. Note: Light reflection and different displays may cause the color of the item in a little different from the real thing. The measurement allowed error is +/- 1-3 cm.