The internal unit for the style H-2 searchlight signal is almost identical to the one used in the style H signal. The outer doublet on the H-2 unit has more curvature being designed to match the smooth outer doublet of the H-2.  There is a notation on the top of each mechanism instructing the signal maintainers which style of signal the unit fits.  The notation reads: Adjusted for style “H-2” signal.  Do not use in style “H.”

While most internal units I have come across have glass bottom covers, some have had plastic bottom covers.  I assume the manufacturers and servicers began using these when quality plastics became available.