Whenever you model an object, you should take advantage of any symmetry that the form provides. It can save you time and effort if you work on only one half of the model and then later copy it across the model’s axis of symmetry. The sketch of the helmet is symmetrical along its center line (YZ plane).

To delete the faces on the left half of the mesh

1. In the top view, right-click on the mesh and select Face from the marking menu that appears.
2. Drag a bounding box around the faces on the left half of the helmet mesh to select them.
3. Press the delete key.

   The selected faces are deleted.

   

You now have half as many components in your model. When you near the completion point of the model, you will copy the finished half across the axis of symmetry to get the complete model.