Du-Bro 2137 - 4-40 E/Z Adjustable Ball Link for 4-40 rod (2)Du Bro Heavy Duty Adjustable Ball Link 4 40 (2) The Du Bro adjustable ball links are heavy duty and include a tension adjustment screw that allows you to torque the proper amount of pressure on the ball. Includes: 2x adjustable swivel ball link (black plastic, self threading for 4 40 rod, 1 1 4" in overall length) 2x burnished brass ball with a #4 hole in it 2x 2 56 x 1 4" roundhead screw for adjusting ball link 2x brass spacer 2x 4 40 locknut 2x 4 40