Jiayouy 4mm 5mm Ball End Truss Rod Adjustment Wrench for Martin Acoustic Guitar Black

Made of carbon steel, durable and highly wear-resistant., 4 & 5mm ball end guitar truss rod, Size:12.5cm x 7.5cm., For locking hexagonal screws on the bridge, adjusting the guitar neck., Two way L-shape truss rod adjusment, 90° Bend no creases, no damage to material., Suitable for Martin acoustic guitar, If use it for other brands of guitars. Please confirm the size of truss rod.