Type 1 stock
Solid Walnut Stock with no grasping grooves or bolttakedown washer. This is the early style stock which was used up until 1915 / 1916

Type 2 stock
Walnut Stock with Bolt takedown washer. The bolttakedown washer appears in 1915, but examples of the type 1 stock continue to be used in 1916.

Type 3 stock
Walnut, or Beech Stock with Bolt takedown washer and
finger grasping grooves. This combination of stock features
appears in 1917, but examples of other stock types continue to be used.

Type 4 stock
Two piece Beech Stock with Bolt takedown washer. I have
a single example of this stock type on a 1915 Erfurt
Kar98a. The stock appears to be a rebuild of a type 2
beech stock. Three other examples have
been described as Post World War 1 Weimar or Police issue.