Table: ar15_variants_2
Columns: colt_model_no
diemaco_model
stock
fire_control
rear_sight
forward_assist
barrel_length
barrel_profile
barrel_twist
hand_guards
bayonet_lug
muzzle_device

Question: Which Barrel twist has a Stock of canadian 3rd generation and a Hand guards of short ribbed?
SQL: SELECT "barrel_twist" FROM ar15_variants_2 WHERE "stock" = 'canadian 3rd generation' AND "hand_guards" = 'short ribbed'

Question: Which Hand guards has a Barrel profile of a2 and a Rear sight of weaver?
SQL: SELECT "hand_guards" FROM ar15_variants_2 WHERE "barrel_profile" = 'a2' AND "rear_sight" = 'weaver'