Concealed under the end-cap, with its spring-loaded clip, is a replaceable eraser.
The bearing is grease lubricated from the spring loaded grease dispenser seen to the right of the bearing.
When unfolded for use, the spring-loaded pliers open to fit your hand.
The optics on this unit are quite superlative, and one nice feature is the spring loaded flip up lens caps.
If you are on a budget but want a more efficient way to nail in the roof, then pick up one of the spring loaded kind.