This is one of Knobbles and Bobbles' beautiful Hexagonal Matt Black coloured knobs.
The diameter of this knob is 40mm and the bolt will fit through a door that is 20mm thick. If your furniture is thicker, you will need to purchase a longer bolt. If it is thinner you might need to put something on the bolt to space it, or cut the bolt to length.
If you have any questions, please email firstname.lastname@example.org.