I use the BFGoodrich style installation tools shown in this installation instruction video...
https://www.youtube.com/watch?v=3jrrf_VbTsc
Standard installation tool PN (for google searches) examples:
C845-440 for 4-40 screws, up to C845-2520 for 1/4-20. For larger hardware, C722-3118 for 5/16-18 through C722-5013 for 1/2-13. Also available in metric, if needed. These are available at aircraft suppliers and elsewhere, shop around for the best prices.
I prefer these tools because they don't rely on a threaded pull stud/bolt spinning inside the rivnut, like some of the cheaper ones. This would risk galling and/or stripping the threads.
For rivnuts, I use the style show in the video that has the splines on the outside to help prevent the fastener from spinning. I get them from McMaster Carr. Part number is 95105A135 for the 10-32 shallow grip, for example..