This is a pair of Traxxas 5x11x4mm ball bearings.  These are used in the clutch bells of many of the Traxxas vehicles.

Features:
Ball bearings reduce friction and last longer than bushings.
Chrome steel construction.
Used to upgrade from bushings

Includes
Two 5 x 11mm bearings

Specs
Inner Diameter:  5mm
Outer Diameter: 11mm
Thickness:       4mm