Rear axle sway bar mount.
I bought a couple of these for my 86 c&c awhile back (different number).
Found this:
F350 - -exc. Chassis Cab w/Sterling axle | E5TZ-5C489-A | O/8500 GVW - 10 1/4" ring gear
FYI It's missing the back half, ubolt, and nuts from the 'kit'
(looks like I was too slow
)
Scott
'
Camano' 1986 F250 Supercab XLT Lariat 460/C6
'Chanute' 1980 F350 C&C 400/NP 435 - Gin Pole
But there ain't nothin' wrong with the radio