RAM Part RAP-101U : Double socket arm mount with two round bases. Both bases have the AMPS hole pattern. Constructed of heavy composite. Parts include (2) RAP-202U and (1) RAP-201U 5.625 inch arm.
Fits many models including
Garmin 172 172c 178 178c 250 250c Fishfinder
Garmin GPSMAP 292 392 492 Fishfinder