Toy construction set

A toy construction set includes first and second construction elements, a pin, and a fastener including a body and a head. Each of the first and second construction elements includes through-holes and grooves on two major surfaces, respectively, of the construction element. A thickness of each groove is substantially the same. At at least one end of each groove, an edge of the groove is curved. The pin includes a body having a cavity and a member. A first portion of an edge of the member is curved, and a second portion of the edge of the member is straight. A thickness of the member is not larger than the thickness of each groove. The member of the pin is fixed in place in one of the grooves of the first construction element when the first and second construction elements are coupled by the pin and the fastener so as to constrain the pin from rotating with respect to an axis of the body of the pin.