The Zebra DelGuard "unbreakable" pencil
Not gonna lie, this seems like a pretty cool mechanical pencil. You can buy the Zebra DelGuard pencil with refill lead here for $7.
The Unbreakable Lead Pencil
This is such an interesting video about the magnificent engineering behind the Zebra DelGuard which incorporates a spring mechanism to prevent lead from breaking when too much pressure is applied.