It's actually a code for batch weights for raw shafts. Each letter represents a certain weight tolerence that that batch will weigh in at. say a full length shaft will be 400.2 grn they will label those as dq while another batch may weigh in at 402.3 and they would label thos as ds.(this is all hypothetical) All it does is help you order another set of arrows within the same weight range.
Hope this helps