what ye mean aboot the ball bearng mate, sorry im having a proper blonde minute here lol
If the ground is solid or wet, and you are pushing down with the probe carefully, it is a little easier to feel it breaking through into the tunnel, with a ball bearing on the end, as the ball is slightly wider than the rebar. When the ball breaks through there is no soil gripping the bar, if that makes sense. It was something I learnt with the smaller version I now use on mole runs.
an excellent post, i've been ferreting 20 years and learnt something new today. makes perfect sense.