Tungsten bucking bars are absolutely one of the best investments you can make if you are building an airplane or do a lot of riveting. Tungsten bars are approximately twice the density of steel of the same size. This bars weighs 1lb 7oz.
This allows you to create a smaller bar that fits in more places, yet has the mass required to give excellent quality rivets. In addition, there is a lot less vibration than a comparable steel bar, which leads to reduced operator fatigue and less chance of injury.