Some of you might like to make your own custom augers. The two main advantages of manufacturing the auger are, 1. Customing auger length and diameter to match available tube ID, and 2. control of auger pitch, and 3. better control of auger to tube clearance.
The attached sheet explains the steps for calculating the OD and ID of the auger flight blanks how to make the pattern for auger flights.
WARNING: you will need to have a good knowledge of metal fabrication to actual make the blanks and for the helix. However the following links will help you make a jig for bending flights and assembling auger.
Auger flight jig and flight bending
Auger assembly

I hope some of you find this information helpful.