Du-Bro 2139 - 2-56 Swivel ball link for 4-40 rod (2)Du Bro Swivel Ball Link 2 56 4 40 with Hardware (2) This high quality ball link offers smooth, secure operation with less slop. You'd want to use this on any control surface where accuracy is required (like the throttle linkage). Includes: 2x swivel ball link (Black plastic, self threading for 4 40 rod, 1" in overall length) with a burnished brass ball pre installed with a #2 hole in it 2x 2 56 x 1 2" socket cap screw 2x brass spacer 2x 2 56 steel nut