modelos extras datos many to many

class Caballeros(models.Model):
   nombre = models.CharField(max_length=30)

class Armaduras(models.Model):
   nombre = models.CharField(max_length=30)
   tipo = models.CharField(max_length=40)
   caballeros = models.ManyToManyField(Caballeros, through='CaballerosArmaduras')

class CaballerosArmaduras(models.Model):
    caballero = models.ForeignKey(Caballeros)
    armadura = models.ForeignKey(Armaduras)
    extra = models.DateField()
    extra = models.CharField(max_length=64)