This is an extremely specific adapter to fit the Fellow flow control Aeropress filter to very specific diameter cups, where the Aeropress would otherwise not securely on top.You can see the problem in one of the pictures, where the filter would just barely sit on the rim of cups with about 67mm diameter. This adapter helps with exactly that edge case of cup diameter.For FDM printing at home this is best printed in PETG as it will see some amount of heat. Does not come in contact with the drink so food safety shouldn't be an issue here.For ordering here, I recommend SLS Nylon or Aluminium if you are feling fancy.