25Pcs Steel Multi Grip Rivet Nuts Pre Bulbed Shank Zinc-Plated Flat Head Threaded Insert Nut Construction Fasteners for Industrial (1/4-20)

These were perfect for repairing broken, rusted out threads in my sewage basin. First, I tried using the rivnuts, but those failed to hold in plastic. Rivnuts seem to not have enough surface grip to work in plastic even if it's thick. These, on the other hand were the perfect solution. The only down side is that the ruvnut tool shank was too short to use with these. They are longer than ruvnuts before they are locked in, so instead I made a custom tool using a bolt, some nuts, and washers. That did the trick. Once locked in, these will not move. Lots of surface area to grip, so even in plastic with strong torque on the bolts, these did not spin once locked in. Strongly recommend.

Much better than the nut serts that I used in the past. Much larger surface area than the smaller ones with the ribs around them.

I installed 6 of the M8 sizes and 1 snapped and the threads on 2 others got damaged. I absolutely do not recommend these.