What is "setscrews"

Usage examples of "setscrews".

All that was required was for Chief Beck—doing much sign language and occasionally drawing with a piece of charcoal on the deck—to acquaint the Chinese with the very basic facts that the propeller had on one side a square opening to fit the shaft, and on the other a fairwater that had to point astern, and around its collar four big setscrews that had to be made immovably tight.