Rivnuts need two things to set properly. The set hole needs to be just small enough so that the ridges on the outside of the part that inserts into mount surface can have metal to bite up on and not spin during installation. The second thing is the part of getting the longitudinal pull on the collapsible part of the nut (which locks it to the mount surface). With a proper tool, the mandrel is first screwed into the rivenut far enough to bite up on the part that makes it collapse and THEN the handles use a straight longitudinal pulling force (without turning up on the threads). This pretty much stops the problem of the rivnut actually spinning in the mount surface while setting it. IMO, the tool should be used if at all possible - they aren't really that expensive. You can do it without the tool but you're depending much more on proper hole size and keeping the rivnut from spinning while you're pulling up using screw turning on the insert bolt.