47. Stacking faults in bcc

Basics of Mechanical Behavior of Materials
This video deals with
1. Slip system in BCC
2. Dislocations and stacking sequence in BCC
3. Stacking fault on 110 planes
3. Stacking fault on 112 planes

[@user-un3on3vp7x]

A&D, C&F, and B&E are in the same position, why bcc {211} not abc stacking?
Also, at 19:50, why after the plane slip, we say the original E plane is now at C position instead of F position?
Thanks for your excellent and helpful videos.

[@nirajchawake]

The abc stacking of 211 alone cannot form a complete bcc unit cell. You need six layers, abcdef, of 211 stacking to complete the bcc structure.
You can also think of it as F, and there shouldn't be any issue with that. However, it's referred to as C because this approach makes it easier to understand twinning in bcc crystals.