915a. 2" long:
915b. Similar to the previous device, 3-5/8" long"
Rotating the piece on the back moves the needle on the front:
916. 2" long:
917. The wooden base is 16-3/4" long:
918. 7" long:
919. 6" tall, please see Neatorama for more guesses on the purpose of these springs, this week Alex is offering a T-shirt for the first correct answer.
920. 5-1/2" long:
Last week's set is seen below, click here to view the entire post:
More discussion and comments on these photos can be found at the newsgroup rec.puzzles.