It looks like a square, but closer inspection reveals a hexagonal shape.
The all-metal polygonal shape, with its restrained corners, is more solid than poppy.
With a small lens diameter, options other than Boston round are rare.

Size:

Width of front: 129mm
Height of the front: 40mm
Width of lens: 38mm
Height of lens: 42mm
Bridge width: 21mm
Temple length: 129mm
*Please allow for slight variations.