Possibly ?? parts from the bomb bay. Mechanisms that controlled the opening and closing of the bomb bay doors.
This link lets you look in various parts of a B-17.
http://vintagetin.net/B-17Nine-O-Nine/G/
Take a look at the regions in the bomb bay, (upper and lower views) particularly at the parts that opened and closed the doors.
There is an electric motor located at the front center of the bomb bay. It drives a mechanism (similar to yours shown in the last three photos) mounted above it and a similar mechanism on the back (rear bomb bay) wall. (Power is sent to the back wall via a rod which rotates in a tube running under the catwalk.)
Each mechanism drives 2 jack screws to the left and right sides of the bomb bay. Those screws go down and attach to the two bomb bay doors (at both the front end and back end) of the left side and right side doors.