Mesh collider is larger than object

Hello , i have encountered a problem where mesh collider is bigger than my object . In last project i created chains using blender , when i applied mesh collider it worked perfectly , collider sticked right on the faces of that chains in any angle. Now i created object with much less faces and when i applied mesh collider ,it created a box that is obviously bigger than the object and it does not bend as faces do , its just square around the whole object. What can i do ?

Many thanks