Abstract: A receptacle for propping the cylinder of a cylinder-and-plunger strut in extended position of the strut includes two side-by-side cylindrical chambers, one being of a size to embrace the jack plunger rod but not the jack cylinder and the other chamber being of a size to slide over the jack cylinder, which chambers are interconnected by a slot sufficiently narrower than the jack plunger rod to enable the receptacle to move into a position embracing the jack plunger rod by snap action, and the larger chamber being of a size to slide lengthwise over the cylinder and having in it a lengthwise slot sufficiently narrow so as not to be able to pass the cylinder through it but sufficiently wide to pass the plunger rod through it.