When I got my TW-6 2 box detector (used) this was in the case with it but I can't find any information for it anywhere. I'm assuming it's a "mini probe" used same as the regular probe but want to be sure.
The tracer probe is shorter than the earlier model, but will work with either the TW-6 or TW-5. It does not need a separate sensitivity knob. It accurately measures the depth of the line you are tracing.
That's all I can think of.
Have you tried calling Fisher and asking....I would.