Which object is being described?

1. It’s got a point at one end and that’s the end you write with.   a pencil
2. It’s a shellfish. It is usually grey, but it goes pink when you cook it. 
3. It can be metal or plastic and you often put water in it to wash floors. 
4. It is usually made of wood or metal, and you climb up it. 
5. At certain times of the month it’s round; at others, it’s closer to a semi-circle. 
6. An adult human body has 206 of these.