Both J nuts and U nuts are clip-on nuts. J nuts, and U nuts are similar but different designs. J nuts is a J-shaped design, whereas U-nuts is a U-shaped design.
When inspecting clip-on nut, you’ll notice that it has two sides,The sides of a U nut are equal lengths. In comparison, one side of a J nut is longer than the other side. From the below picturer , the top one is U nut with same lengths, the below one is J Nut with different lengths.

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