This is a handle for a shaving brush. You will need to purchase a knot from a reputable source, such as :
You can find videos on youtube which demonstrate how to install a knot into the shaving brush handle. You may need to remove some glazing from the knot cavity, depending on the epoxy that you choose to use.
The cavity in the handle is 26mm diameter, 15mm deep, to accommodate a 24mm knot.