Mother of rivets

You’re describing a metal flat head threaded insert rivet nut assortment set with these features:

• Material: Galvanized iron (offers corrosion resistance).
• Type: Threaded rivet nuts (also called rivnuts, nutserts) with a flat head for flush mounting.
• Body: Knurled — improves grip inside the sheet metal to prevent spinning after installation.
• Application: Ideal for:
  • Sheet metal
  • Automotive repairs and modifications
  • Furniture assembly
  • Decorative projects
• Installation: Installed by pushing/threading into a pre-drilled hole, then compressed or “riveted” so it clamps tightly and provides a strong, reusable threaded hole.

These kits usually come in various sizes and thread types to fit different screws and bolts.