These companies need to make a universal fit for all similar sized tanks.
Something like these which fit Smok Aro, TDux 1,2,3 and Kanger Pro-Tanks 1,2,3, Kanger Evod style tanks and various other different company's products?
Also in agreement with the below:
We have: it's called Nichrome, Kanthal & Stainless wire.
Spinning up
basic coils isn't difficult to do and using what are called "macro" coils in RDA/RDTA/RBA is pretty simple and straight forward. Anything with an inner diameter of 2.50+ mm is what I believe most consider a macro coil and 2 to 0.5 mm inner diameter is micro coils. Like macro coils myself as arthritis, nerve issues foul with me having patience to use micro coils. A bit more bearable and easier to fidget with bigger coils. Added benefit, sub-ohming does well about 93 to 99 percent of the time for me.
You might want to use a guide like
Steam Engine. It helps having a reference point to start getting a good idea and feel about what number of wraps gets what ohm rating. After a bit you gain a quick memory from experience to do by. Still suggest spot checking yourself with an ohm meter every so often, keep it random to keep your spinning coils honest. I usually aim for around 0.30 to 0.35 and get some what may read at 0.4. I'm still in the "safe range" I've figured out suits me, that's 0.30 to 0.50 ohms. I use that range of coils for both mechanical and regulated mods.
But also, you don't need to make your own coils. Yes, plenty of good reasons to do so. You can though keep using pre-made stuff. You'll be stuck with what you're given though. If you cannot get coils for whatever kind of tank, rda, well then you'll need to use another kind of tank or rda. Sorry but it's that simple really. You got to accept your choice and even know if you don't choose you still make a choice.