A composite tube assembly may comprise a composite tube comprising a radially outer surface having a variable diameter portion comprising a first frustoconical portion and a second frustoconical portion, a locking wedge disposed at least partially around a circumference of the first frustoconical portion, a locking collar nut disposed at least partially around a circumference of the locking wedge, and an end fitting disposed at least partially around a circumference of the second frustoconical portion, wherein the end fitting is coupled to the locking collar nut. A diameter of the composite tube, at an interface between the first frustoconical portion and the second frustoconical portion, may be a maximum diameter value with respect to the first frustoconical portion and may be a maximum diameter value with respect to the second frustoconical portion.