A skateboard may include a pair of foot support boards connected by a torsion bar connecting element, a torsion bar cover tube mounted to the foot support boards and surrounding at least a portion of the torsion bar connecting element and an outer tube mounted for rotation around the torsion bar cover tube in response to contact with an obstacle. The cam member has the cam surface provided with a protruded portion which comes into contact with only a portion of a side wall of the cam pin. As such, when a wheelchair is rolled over the pedals, the threshold automatically flattens to facilitate unimpeded entry. The soft material of the member to be joined, which is located in a circumferential direction of the member, bites into a joining portion of the joining member by the plastic deformation and with the elastic deformation pressure. Through the present invention, an issuing device may transfer the licenses issued by other issuing devices, thus improving the flexibility of transferring the licenses. Thereafter, crosslinking agents are added and the water is removed from the emulsions providing siloxane crosslinks between the two intimately mixed immiscible phases.