Uphold Cutlery is a ridiculously small folding travel cutlery to help eliminate single-use plastics. The colour of these two sets is GUNMETAL (see picture).
The polymer used for the folding connection is TPU/TPE, which is a relatively new type of hard plastic with rubber properties. It is strong, yet flexible enough for it to bend and fold. It has similar physical and machanical properties to a common plastic polypropylene (aka PP), known with the nickname 'multifold plastic', and can bend repeatedly along folding hinges and does not tear nor shatter.
The fitting method is called 'interference fit' (or 'friction fit'). If you look at the construction of the utensil parts, the head side connector is polymer and the handle side connector is metal. As polymer is 'softer' than metal, the polymer end will 'give' when the metal handle is inserted, creating reasonable friction that will resist it from moving, let alone dropping off. A reference to this type of fitting would be a plastic brush head onto the metal shaft of an electric toothbrush.
Besides from convenience, the single biggest factor that deters users from using travel cutlery is its portability. Uphold Cutlery is market-leading in its weight and volume in travel cutlery design. In a direct comparison*, it offers the lightest and slimmest solution amongst products that offer similar utility.