These are Milspec heavy duty 12/3 STW 600V extension cords, (White)

with Pro Cap outlets spaced at 10' intervals to allow multiple portable tool uses along the length of the cord.

The individual Pro Cap outlet covers keep out dust, dirt and moisture.

Converts a single outlet extension cord into three (3) standard 15A-125V grounded outlets at 8 ft. intervals on a 25 Ft. cord and five (5) outlets at 10 ft. intervals on a 50 Ft. cord. 
Clear neon lighted connectors indicates that there is power in the circuit.