This is an 8ohm horn tweeter used in a few different models of B-52 speakers.  If you need a replacement and it looks like this, it is this.

horn is 7x7 very rigid and thick with 50x80 elliptical dispersion pattern for a very smooth response

4 3/8" mounting depth

5 1/8" overall depth

8 1/4" diagonal screw spacing to centers

minimum cutoff of this waveguide is 1500Hz.  For high power use, the recommended crossover is 2khz or higher at a minimum of 12dB/octave slope