This looks like it may be some kind of potentiometer, or variable resistor. Aluminum casting with two bolt holes, on stepped ears for surface mount. One of the ears has the name(?) RACO embossed in the casting. Two 5mm threaded (electrical) connection posts project from the top. One is isolated (insulated) from the body by non conducting grommet, except for a thin, solid wire wound around the casting (10 wraps/cm, over 6cm, or 60 wraps) and connecting to the opposite post. There is a bridge over the wraps with a thumbscrew locking, adjustable slide that appears to shunt from a variable position on the coil, directly to the opposite pole. The bridge has a slot cut out allong center to accomodate the slide. the top of the cut-out is marked:
N MAX
1.22 603-6 12.5
The lower bar is a linear scale from 1 to 10, with the start position, #1 is off-set from the LHS, by approximately slightly wider than the sliding contactor, directly below the first 2 in 1.22. This is a significant component (part) found along side of infrequently used rail-road track.
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