posd = models.ManyToManyField(Posd, through='Posd', through_fields=('hg','pos')) # This is wrong, doesn't work

class Posd(models.Model):
#This class is just repsresenting the cost position in KBSUMME
hg = models.IntegerField()
pos = models.IntegerField()
description = models.CharField(max_length=200)
hours = models.CharField(max_length=5)
cost = models.CharField(max_length=5)

class Meta:
    unique_together = (('hg', 'pos'),)

class KbMeta(models.Model):
#This class is representing the meta data for one project. One row per project only.
pid = models.IntegerField(primary_key=True)
klaversion = models.CharField(max_length=50, blank=True)
calcbase = models.CharField(max_length=10, blank=True)
contractbase = models.CharField(max_length=10, blank=True)
quotno = models.CharField(max_length=50)
filename = models.CharField(max_length=100)
datecalc = models.DateField(default='1999-09-09')
dateupload = models.DateTimeField(default='1999-09-09')
projname = models.CharField(max_length=100, blank=True)
customer = models.CharField(max_length=100, blank=True)
endcustomer = models.CharField(max_length=100, blank=True)
phase = models.CharField(max_length=50, blank=True)

class Tdb(models.Model):
#This is the T detail cost calculation
hg = models.IntegerField()
pos = models.IntegerField()
hours = models.FloatField()
cost = models.FloatField()
kbmeta = models.ForeignKey(KbMeta, on_delete=models.CASCADE)
posd = models.ManyToManyField(Posd, through='Posd', through_fields=('hg','pos')) # This is wrong, doesn't work