Got some bottom feeder pins from fatdaddyvapes and converted a Petri clone. It takes the 2.5mm pin. Drilled up thru the 510 with a 1/16" bit into the chamber to avoid damaging the female threads. Then down from the chamber with a 5/64" bit to enlarge the hole so the pin would fit thru into the chamber. The Petri has some kind of baseplate/insulator thing which complicates matters a bit. It's working good, I really like this dripper. Only issue is the heads of the hollow bf pins are too long, so the atty doesn't fit flush on the mod and there is a small gap. Was considering (and may still do it) filing the head down, but it needs to fit flat and flush against the 510 mod pin so there is no leaking, and not sure my filing skills are up to that task.