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The suspicious gold bar is a junk item in the Fallout 76 update Wastelanders.
One of three impure gold bars, having been alloyed with lead, requisitioned and stolen by Private Miller for an attempted scam.
The suspicious gold bar can be broken down into its individual components for use in crafting:
Found in a shopping cart, along with the dubious and questionable gold bars, as part of the Fake Gold Bars random encounter.