I'm glad this has come up again, as I have been wasting a lot of thinking time considering this recently without a truly satisfactory solution.
I've done both drilling a brass screw,and drilling the original plain FD brass pin brass to just under 1.8mm to get a nice stiff interference fit for the pin, this is on the V4 with standard core (the stainless vented screws are over $50 for ten if we buy on amazon here in Oz, so haven't tried them), and I've also used the V3 with the already OVERDRILLED BF brass contact,and the use of glue (not ideal, but preferable to solder is the ss pin is not and has the flange cut off so the brass pin contacting the atty pin) to fill the void between the hole in the brass contact pin and the ss pin.
My thoughts are this, (I predominately use Igo-L's drilled, and modified by grinding a dish in the well, they seem to be about in the middle as far as pin length)
for a MOD THAT I AM GOING TO ONLY USE MYSELF, I have no issue (well almost none but i will get to that later) with either setup, as most of my attys are going to fit without any adjustment,on the other hand if the mod is for a friend or less experienced vaper/modding minded person, then the drilled screw method begins to look like a pain for the mod maker, want we want is a close to 100% reliable system that does not come back to us with problems and leaks, having to loosen the positive connection to adjust the pin height is not a good look when explaining this to a new user, and could lead to a failure or broken part in this area.
With the drilling of the original non BF pin in the V4 core you want a 1.75mm drill bit, and you will be all good for an interference fit with the pin, I only had a 1.6mm and it took some careful enlarging of that hole after the initial drilling, I found however that I needed to add an extra o-ring to the V4 core to get a firm enough feeling connection with the Igo-L, but i have had ZERO leaks on that one and I don't have any solder to consider, this is how the proper BF pin setup should be IMO, a decent interference fit out of the gate. I do however have two small issues with this set up despite it's relatively effective self adjusting advantage.
No1. the interior of the ss FD pin is tiny, maybe 1mm and this does not lead to effortless squonking, which takes away from the pleasure of it's use, the ID needs to be around 1.6- 1.8mm to offer little or no squonking resistance, this is the hole size in mt drilled brass screw and the squonking action is sublime especially with the Vapage XL bottle.
My last gripe with this setup is with the positive connection or inherent lack of a decent one and the space swallowed up by creating one,soldering dirrectly to the brass core pin on the V4 is more practical than on the v3 but it's still not ideal at strip down time, having to screw in unscrew the core is a fiddly procedure with those fine delrin threads, and is not fun with the connector in situe inside the box, so a clamping collar is the only real alternative and this swallows up around 3-4mm of space in area I am constantly struggling for space. As I write this i am thinking that soldering directly to that brass pin could be much more compact in this last regard and assumming your interference fit is good enough you have a choice to either use the SS top flange as your contact point with the atty or cut it of and just use the shaft of the ss pin for an internal liner for the brass pin, although this would definitely require the extra o-ring as you would end up with a looser connection at the atty otherwise.
So what is the ideal solution? In my mind it would be fairly simple for FD to implement. A longer brass drilled BF pin with the same size hole as presently (around 2mm) and gold plate it for the most low profile option, to be soldered at the pos connection. For a more versatile but more space hungry alternative, we would want the same thing, but with a threaded section to take two clamping nuts and enough space or a 0.4-0.7mm plate to be clamped by said nuts, add to this two extra o-rings for adjustment and we would be in business.
The other reason I don't really want to go with the classic FD 510 is the lack of plain 22mm flat top that is available in the V4, and although not plain the V3 has a 22MM option with the upsizer ring.
Brass contacting juice isn't just about the proposed health issues some are fearful of (not me) it's a conductivity drop when green and gunky and it's cleaning issue, gold plating for such a small item would be such a small additional cost for a large batch, and in return we would have a truly plug and play and forget system, the small silicone o-rings that go inside the connector from the top work well in some instances, but as a last point an o-ring channel in the top of the connector would also be a welcome addition.
All this does rely on O-rings and although not a lifelong reliable part, if correctly installed set up they allow for the all important flexibility to adjust to very slightly different length atty pos post without user input and still retain a good seal for a long time, and can be replace should they need it.
Just my
