These are made of plastic.
One seat belt stop button comes in two pieces/halves. One half has a pin and the other half has a hole.
-It can be installed with a pair of pliers. Push the pin through the belt, put the other half over the pin, carefully press the end of the pin straight in. Don’t let the end of the pin bend over.
-Once pressed the pin will swell and hold the halves together and the end of the pin will be flat.
-It may also be installed with a soldering iron by melting the point of the pin.
The halves do NOT snap together.