Sentence:  The return spring tension may be adjusted to suit individual requirements by gripping the spring housing with a pair of pliers ( to <WSD>prevent</WSD> the spring from unwinding when it is released ) , loosening the lock nut or screw , and rotating the housing until the desired tension is achieved . 
Meaning of the word marked with <WSD> tags:  stop (someone or something) from doing something or being in a certain state