Abstract: An adaptor bracket for rotatably securing a retractable lifeline block to a corner casting on a cargo retaining frame wherein the bracket has a locked position when it is secured to the corner casting and an unlocked position for removal from the corner casting. The bracket includes a twist lock which is spring-biased such that insertion of the twist lock into an opening in the corner casting automatically turns the twist lock to the locked position. Manual pressure and rotation of the twist lock placed it in the unlocked position for removal from the corner casting. The adaptor bracket and the retractable lifeline block are rotatable relative to the corner casting when in the locked position. Also disclosed is a standard method of using the adaptor bracket at a work site.