In-Line Fuse Holder - Yellow Bussman Eaton Waterproof Fuse Holder, Buss Fuse, & Lugs - RR21001

Perhaps this was part of an installation kit for a radio? Along with the inline fuse holder, you'll also receive a Buss AGC 3A, 250V fuse, & 3 wire lugs.

Inline waterproof fuseholder for 1/4" x 1-1/4" (6.35 mm x 31.8 mm) fuses.
Accepts #16 to #12 AWG Cu wire
IP67 rating for exposed locations & ideal for harsh environments
Vibration Resistance: Per MIL STD 810C
Temperature Rating (RTI): +100 °C
Brittle Point: Less than -60 °C

Full product specifications for this BUSSMAN Series product from Eaton.