This is a Vintage new old stock KD brand 5" round yellow marker light. Model KD-538.  Painted steel housing. Single filament bulb. Unused but does have some chips and scratches in the paint. 2" spacing on mounting bolts. Lens says STRATOLIGHT. Has number SAE-S-IA-T-68 on it. Tested working.  Rare hard to find style. See pics for details. Thanks for looking.