Furuno FM-2721 Operator's Manual page 16

For bulkhead mounting, tighten upper tapping
screws (supplied) and washers so there is 5 mm
clearance between bottom of screw head and
240
bulkhead, and screw slots of the unit. Then fasten
upper screws and washers.
4- 5 Fixing Hole
Transceiver unit, top and side view
2
200