I really like the varitube. The length of the threaded part isn't uber long, so it's easier to fit in a box. I also really like the design if the positive pin. The spring doesn't carry any current. It's super easy to get a wire soldered to it. You take your wire, slip over little cap, slip over the spring, then there's a top hat thing. The top is what makes contact with the 510 center. Just tin up the wire a little, solder it into the top hat, slide over a delrin threaded sleeve, tighten down the cap onto the sleeve with the spring between the top hat and the cap and voila. There's very little risk of it shorting. Plus it costs a little
Less.