Might just be that the gun makers had another pricey gadget to sell as a “had to have” item since there were no visegrips for sale back then Hey? Seems like I read once that the turn screw vise was used just to keep some compression on an “ in use “ spring while removed from the lock. Old springs could begin to develop micro cracks at the bend when left fully relaxed since they normally have some compression on them at all times while installed. So..It might also make your spring last longer. Makes sense to me but hey...I’m just an old retired maintence guy so what could I know?