Review on 🔩 Rivet Nuts Assortment Kit: 150Pcs 1/4"-20 3/8"-16 5/16"-18 UNC Nutserts, Flat Head Threaded Insert Nuts+Knurled Body (M6 M8 M10 Carbon Steel) by Jonathan Devarapalli

They are strong and the threads are solid. If used in softwood or plywood they are fine, no problem. When using with hardwoods (especially oak) I had trouble getting the insert all the way in without removing the hex (wrench) portion of the insert. I've tried making the mortise hole a little larger with a drill but not very well. I was afraid to go up a size, I have limited size drills and would have to go for a full size 16. In the end I managed to drag them all into my project and everything worked out, just a little harder than on a fir tree.