A Galaxy-class starboard nacelle pylon.
A nacelle pylon, also known as a warp pylon, a pylon and also a nacelle strut, was a large support beam that connected a warp nacelle to the hull of a starship. A nacelle pylon housed the systems that were directly connected to a starship's warp core.
While attempting to break the warp 10 barrier in a holographic Cochrane in 2372, Tom Paris reported a fracture in the port nacelle pylon due to subspace torque. Later, after the problem had been corrected, Paris broke the barrier with both pylons secure. (VOY: "Threshold")
In an alternate timeline in 2374, USS Voyager's nacelle pylon began to buckle as a result of encountering a micro-meteoroid shower while operating without the use of its navigational deflector. (VOY: "Year of Hell, Part II")