This is the Axial OCP Rear Full Width Axle Adapter Set.

Works with AR60 OCP axle
Steel axles with black oxide coating to resist corrosion
Aluminum hub carriers

Two Axles, AXIC0775
Two Hub Carriers, AXIC0833
Four 5x11x4mm Ball Bearings
Three 3x5mm Screws
Instruction Sheet

Short Axle Length: 4.5" (114mm)
Long Axle Length: 6.7" (170mm)
Diameter: 0.18" (4.6mm)