This is the wireless 5 gram micro flashing navigation set by Radio Controlled Models, Inc.
Features: The RAM 188 is designed to provide a bright, light weight (5 gram), navigation system that results in easy orientation during low light, at evening or at night when flying conditions are ideal for ultra-light models. They are also helpful to keep orientation in daylight. With included batteries, these LEDs flash continuously for up to five days.
Length: 25.5mm (1)
Width: 22mm (7/8)
Thickness: 4.7mm (3/16)
Battery Diameter: 12.5mm (1/2)
Battery Thickness: 2.0mm (3/32)