This is a Robart right strut for a 3-3/4" to 4" wheel.

Replace your wire landing gear struts with units that duplicate the shock absorbing action of landing gear on real aircraft - Robart's Robostruts. This gear can smooth out bumps & hard landings, improves ground tracking, and pro- tects your valuable landing gear from shock damage. These Robostruts are scale or semi-scale in appearance, which makes them perfect for your 12-15 pound sport, scale, or jet. They can also be retrofitted for your retract system.