Jib Car
From MITNA
The jib car, or jib lead, is a block through which a jib sheet is run.
The position of the jib car can usually be adjusted forward or aft and is often mounted on a track on the deck. Moving the position of the car changes the angle that the jib sheet makes with the clew of the jib sail. By changing the angle of the sheet, you can adjust the amount of tension on the foot or the leech of the jib sail, which adjusts its draft and twist.
