A pair of replacement whisker antenna. This is the same antenna that the props chopped off your receiver. Fits the X4R-SB, D4R-II, S6R etc. Connector also fits R-XSR, XM, XM+ and Archer RS but the unshielded tip length is different than the original antenna.
The active element in the antenna is the unshielded part at the tip - if you have lost any of that portion of the antenna it's no longer tuned to 2.4GHz and should be replaced.
This is the new IPEX4 style connector. Production changed around August 2016. The older IPEX1/U.FL connector has a diameter of ~3mm. The newer connector has a diameter of ~2mm and uses a thinner wire.