Hi Guys, I am Derek McLennan one of the Equinox development testers based in the UK, Scotland to be precise and as I have an old X-Terra 305 and the Equinox, I thought I would let you know the answer to your question. The short answer is that the X-Terra bottom stem will fit as it is around 1mm smaller in diameter than the corresponding female end socket of the Equinox stem. This obviously leads to a bit of movement in the bottom stem, but this can be taken up with the tightening mechanism on the Equinox stem, but I am unsure how strong or stable this would be longer term or within some specific detecting environments (e.g. stubble, rough plough, rocky ground, surf, underwater, etc). There is another issue though and you will find that the ball bearing locking pin does not fit into the Equinox locking hole on the middle stem - the X-Terra ball bearing is obviously slightly larger in diameter than that on the Equinox. So, this may in turn lead to even more loss of joint stability and the X-Terra stem rotating during operation while attached to the Equinox. I have attached some images for you and hope this helps.