These are stainless steel pin backs / clutch backs with rubber discs.

They’re typically used for securing lapel pins, badges, brooches, tie tacks, or enamel pins.

Here’s a breakdown of what you’re seeing:

• Material: The metal part is stainless steel, which resists rust and tarnishing.

• Design: The back is a standard butterfly clutch (sometimes called a “locking clutch”) but with a clear rubber or silicone disc added.

• Purpose of disc: The disc increases surface area against fabric so the pin sits more securely and doesn’t sag or tear thin material.

This style is common for higher-quality or heavier pins, especially enamel pins sold at shows or in collections.