These are working brick stud knobs to decorate anything which has, well, a knob!  Much more fun than those boring plain ones you got with the furniture!

Because bricks are made to such a small tolerance, you need to get the right size studs first.  I recommend you do this for each printer you use and each different filament; I've found they can vary greatly between manufacturers.  I made all mine in PLA+.

1. Print the 5 test piece plate first.  Each piece has a letter A-E cut into it.  The knobs are a tiny bit different-sized on each one.

    

2. Try them all with some bricks, preferably ones which span all 4 studs.

    

3. Once you've worked out which one is best in your combination, pick the plate with the right knob on it (the letter is embossed into the bottom of each one in case you get lost) and go mad!  They print stalk-down and don't need supports.

    

4. To finish them, you need M4 x 6mm L x 6mm heat-set knurled brass inserts (which Bambu have) and M4 x 25mm cupboard knob screws (which they don't), and a soldering iron preferably with a rounded tip.  If you can't get knob screws (they have a built-in washer to stop them going through the hole in the cupboard door) then get some thin M4 washers and use those.  You might be able to reuse the ones already on your doors, have a check.

    

5. Put each knob face-down and balance a brass insert on the central hole.  Keeping super vertical, rest the (heated!) soldering iron on the hole in the insert and apply very very gentle pressure.  After a minute when the metal is warm enough, the insert will start to sink into the plastic.  Go slowly and keep straight, and stop when the insert is just below the top of the plastic.  It doesn't matter if you go a tiny bit too far, but don't leave it sticking out.

    

6. Take the old knobs off, new ones on, job done!