The ultimate nuker is crafted from the 3 other ingots. einsteinium,neptunium , and uranium ingots. It's explosion is 100. Here is a picture comparing the bombs from TNT, and each other. This is a custom modeled block.
It's a bomb, so it's used to blow things up. This is the highest tier of the bombs (Not including TNT). As of beta 1.9 and up, you have to use a redstone signal to set it off, since it is made of metal.
Added where you can set the bombs off with a gelid redstone torch.
Bugs
Bug; Beta 1.5 - 15w22a: When activated, it goes invisible.
Trivia
The color of the name for the block is gray.
This is the highest tier of the bombs, not including TNT.
If you notice, from uranium bomb to this one on the tool tip, it skips a star. This is because there was a nuke that was added, but was never really in the mod. Then MCE's pc crashed and he had to redo the mod, and it wasn't added in again. This is also why this block is called the ultimate nuker.
You need to use redstone to set it off, it makes sense because it's made of metal.