I was digging around the Kidney Puncher website last week and found that they sell a "BDC to Protank Adapter" and decided to give it a whirl. I've always liked the Aspire BDC coil heads and figured it was worth a shot for the whole $3 or so that it cost. Basically what the product is is an extension ring that sits between the Protank tank portion and the base portion that usually screws into the tank. It lengthens the entire tank by about a little more than 1/4". That is enough to accommodate the distance that the center tube needs to be pushed up to fit the BDC coil under it.
I was shocked to see that the BDC coil just screwed right into the Protank base. Who knew Protank heads and Aspire BDC heads used the exact same bases? Welp. They do. The adapter comes with one tiny plastic grommet that sits between the BDC head and the center tube and I'm assuming helps to prevent leaking into the head. I saw that Kidney Puncher offered an additional set of 5 grommets for a couple bucks more so sprung for those as well. As you can imagine, the grommets are tiny and without them, you are pretty much out of luck. Here's what the whole thing looks like.
Would I recommend this to anyone over an Aspire tank? Probably not. But if, like me, you have an unused Protank sitting around and you like the Aspire coils, this is a pretty good, pretty reasonably priced solution.
And it was pure bonus that Kidney Puncher had Nautilus coils in stock at a dirt cheap price. They have a great many products like this one that you simply can't find anywhere else. Shipping cost was low and got here quickly. I'd gladly order from them again.