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A line-replaceable unit (LRU) is a modular component of an airplane, ship or spacecraft that is designed to be replaced quickly at an operating location. An LRU is usually a sealed unit (black box), such as a radio or other auxiliary equipment. — “Line-replaceable unit - Wikipedia, the free encyclopedia”, en.wikipedia.org
A Field Replaceable Unit or FRU is a circuit board, part or assembly that can be quickly and easily removed from a personal computer or other piece of electronic equipment, and replaced by the user or a technician without having to send the entire product or system to a repair facility. — “Field Replaceable Unit - Wikipedia, the free encyclopedia”, en.wikipedia.org
Such images should be speedy deleted, per speedy deletion criterion #7 for images or media, if no one has made a convincing argument for why a free licensed replacement can not be created within a week of the image being flagged as replaceable. — “Category:Replaceable non-free use Wikipedia files - Wikipedia”, en.wikipedia.org