This is the TRF Aluminum 4mm Turnbuckle Wrench from Tamiya.

FEATURES: Blue aluminum grip with durable steel wrench section For use with aluminum turnbuckle shafts

INCLUDES: TRF Aluminum 4mm Turnbuckle Wrench from Tamiya

SPECS: Wrench Size: 4mm Total Length: 3.3" (83.5mm)  

BOX DIMENSIONS: 2.13" W. X .38" H. X 3.13" L. BOX WEIGHT: .03 LBS.