Nickel free snap buttons.
The buttons consist tow ring, a female and a male.
Dimensions: 11mm fits in the Prym with the "white plumps"
The spikes are a little longer are the "regular" buttons on the market.
Which makes them sit better in slightly thicker material, perfect for eg 4-fold edge band.
Also works in thinner material, the spikes do not penetrate to the other parts.