The BL2 enclosure was designed to house the BL2 board as built per the Elecraft instructions, with the rubber feet mounted on the bottom of the PCB. The BL2 board is secured to the bottom of the enclosure via the thumbscrews at the rear of the board as well to the top of the enclosure via the BNC connector with a supplied hex nut and lockwasher.
1/8" vent holes are drilled in the sides to allow horizontal ventilation. Again, for field use, it should keep most things out. There are also 4 plastic feet on the bottom that grip solid surfaces very well.
The board is secured to the enclosure via the thumbscrews on the back as well as a hex nut on the BNC connector on the front.
Two holes are drilled in the sides to accomodate using
something like a pencil to select the 1:1 or 4:1 switch