Difference between capillaries and veins simplify

Here's a simplified difference between capillaries and veins:

• Capillaries are the smallest blood vessels, with walls only one cell thick. Their main job is to allow the exchange of oxygen, nutrients, and waste products between blood and body tissues.
• Veins are larger blood vessels that carry deoxygenated blood (mostly) back to the heart. They have thicker walls than capillaries and often contain valves to prevent blood from flowing backward.