Ah yes, so-too did mine have a slightly different loop look. Which makes me wonder if there was a difference between the 66T and the 66TR. Looking at old TH'ing magazine ads, it appears that Whites continued to sell the 66TR even to as late as about 1974.
To answer your question, it has little to no use now. About the only possible exception would be if someone wants to "see through" nails. Because those old TRs did have the innate ability to not only null over small iron, but also to see a conductive target beneath them (to a certain degree anyhow). Unlike today's high-powered deep-seeking machines which ..... when they disc. out a nail, risk missing a coin UNDER the nail (ie.: "masking"). Hence those old TRs were good ghost-town machines, where carpets of nails riddled the surface.
HOWEVER, the benefits end there. In all other ways it is a dinasour. To the extent you could "see through nails", it would only do that to a few inches at best. And lacked any other form of TID. And was a bear to keep balance, worked lousy in minerals, etc... And also: The compass 77b (another all-metal TR machine of the same era) did the trick much better, IMHO. And so, to this day, there are some people who still use the 77b for certain nail-riddled environments (under porches of old houses, ghost-townsy type spots, etc....). So too would the 66TR do the same thing. But not quite as nice and smooth as the 77b did, IMHO.
