Easy to get spoiled by an electric nail! I know I sure have starting with the one mockup Growgeek and I assembled, which led Son I to mount the controls in an surplus electrical kit box, and which unit I continue to use to this date.
I did have to replace the heating coil once, after the thermocouple failed, but it essentially stays hot all day, every day, during the waking hours that I'm home, and the coil lasted at least three years. I ordered two replacements and am still on the first after a couple more years.
I've used an Oil Coil thus far, but couldn't locate a ready link to buy more, checked the internet and notice that Aqua Lab Technologies offers replacement coils, as do others. Here are three links to check out:
We used a 20 mm coil, which just slides over a KO V-1 Domeless nail, which was donated to us along with a V-2 for testing. The V-1 is heavier walled and they are straight, where the V-2 has thinner walls that bell outward a few degrees.
KO V-1 Domeless Nail
KO V-1 Domeless Nail in Skunk Pipe
We used a Mypin Model TA4-SSR PID controller and a 25 amp Fotek Solid State Relay:
Mypin TA4-SSR PID Controller
Mypin TA4-SSR wiring diagram
Electric nail schematic
Growgeek and my first test sled
The test sled worked well and my intent was to follow through with a conventional design where the heating coil stays attached to the nail, such as this Bee Nail.
Commercially available assembly
After Son I mounted the controls in and electrical box and we had a chance to use it some more as was, the more we came to appreciate being able to just lift the coil off the nail and pass the pipe across the room, without having the umbelical wiring stringing along.
E-Nail heated and ready to use.
Mypin PID controller in electrical kit box.
Heating coil lifted off of nail to allow it to be passed: