Can i use regular fluorocarbon line as a leader?

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Yes, regular fluorocarbon line can be used as leader. 
Fluorocarbon line is obviously intended to be used as your main line, this is why you will notice that it’s very limp compared to fluorocarbon leader material. 
The resins used to make the leader and the line are often different, so you will see differences in stiffness (leader is stiffer) and abrasion resistance (leader is generally more abrasion resistant).