You can use a bolt or nut with a 13mm head. The hole diameter is up to 8mm. New, unused, and unopened, but there may be some scratches from storage. Bolts and nuts are not included, so you can use bolts of your preferred length. The knob size is approximately 40mm, and the thickness is approximately 18mm. The caps are red, and it's a set of 10 including shipping. Suitable for making portable outdoor tables and shelves. Also for making beds and shelves for cars. Securing covers and cargo boxes for motorcycles. I think it can be used for various DIY projects. You can tighten it firmly without tools.