The first picture shows the stringers which are made from the same material as the spar cap doublers. They attach to the ribs and start by getting attached to each other and the two inboard ribs via the center web section seen in the second picture.
Kathy also did the edge work on the stringers. She is doing a lot of this type of work along the way. The last two pictures show all the flange holes getting countersunk for all the dimpled skin holes where the spar and skins will attach. Both spars and the stringers needed this work which is about 450 countersunk holes to be drilled.
