You'll print layers and assemble them onto your handle. I used a bamboo skewer for one. If you want you can also print a custom central post which can include a key setting so adjacent bristle layers can be spaced out regularity.  I've put in a tons of parameters so you can change how stiff you want the bristles to be and spacing etc.  You do not need to print the center part if you don't want to, see photos of the brush parts I just stuck on a bamboo skewer. The center part was something I decided I wanted when I was worried about the spacing of the layers with each other.Make sure your bed is level and be very gentle removing the parts, especially with thin bristles.  for thin flexible bristles choose:  //bristle width=2 x Nozzle size  //bristle height= 1st layer height  increase values for stiffer bristles.  If you are making a stagger bristle brush, you will want to use the key setting under central post. Notice on the bristle parts there will be notches made in the center support corresponding the the part number. So 1st part has one notch, 2nd part has 2 notches, etc. I choose to also print my layers in different colors to help keep them straight.https://youtu.be/Aby2HPzYXs4