I ordered some of these and they just came in yesterday. They are a smidge too big and really hard to get into the hole (protank is what I'm rebuilding). If you can get them in the base is too wide and has to be trimmed down or the coil assembly won't fit in the base. Squeezing them into the hole while keeping the wires in place proved to be very difficult for me.
One thing I did try, and may work... Make 2 cuts in the insulator down the side and take about a 1mm wedge out of it (maybe a little less). This means its not an intact circle anymore, but makes its circumferences small enough to fit down into the hole. It also makes the base small enough so that it doesn't have to be trimmed. I'd imagine you'd have to be careful that the two wires coming down are not aligned with the section that has the slice cut out of it. I just made a coil like this, and tested the ohms. It came out at 2.1 ohms, but I haven't tried to use it yet. I'm assuming it doesn't have to be an intact circle as long as it is insulating the wires, but could be wrong.
Here is a picture of how I cut the insulator. After the first cut, you'd do a second to take out a thin wedge.
Here is a coil rebuilt with the original insulator (top) and one with the kidney puncher insulator (bottom). If you look closely at the bottom insulator you can make out where the sliced out portion is.
Getting the sliced insulator into the hole of the coil assembly is a little difficult, but not as difficult (IMO) as getting the full sized one in there.
