It's a silicone bung with holes in it for the copper tubing and the thermometer.
It is an $8 coil of copper tubing from DIY store, I only used about half of it. No particular length, I was just experimenting and this looked about right. Lucky for me the coil and computer fan provide plenty of cooling power. I adjust the heat input by touching the coils; for slow runs only the top two are too hot to touch, for stripping runs only the bottom two stay cool enough to touch. As the run progresses I dial up the heat and check the coils as a guide.
No, I use a bigger setup for large batches and making neutral. This is for small batch, recipe testing, and running 40% neutral + botanicals for gin or other flavored stuff. I seriously wouldn't part with this thing for less than a few hundred bucks, and I'd just turn around and build a fancier version of it. It produces really excellent flavors and with the 3L flask I can produce two bottles of gin per run.
Here it is with a doubler, just testing it out.
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Only PITA I guess is that I have to clean the coil periodically or I get a bit of green distillate. I use a tiny fountain pump and circulate hot vinegar solution. Stainless would be ideal but it would need a longer coil to work as efficiently as copper.