vent holes. copper terminals. adj phasing so the arc swing is equidistant with dead center on the terminal if using vac adv and that is the only system that changes phasing in operation & in a killer setup I'd actually like to have the terminals (their operating arc) the closest at WOT (no vac) when the required voltage is the greatest) but with the gap reduced having the arc distance centered is OK & far better than it was prior. Burning comes from high resistance which is not the issue in a dist cap (one that ain't carboned up) and the other is gap which is always present in a dist cap by its' design but minimize it by reducing the rotor blade tip to cap terminal clearance to .015" (best). NAPA has an Echlin rotor MO3000 with a .060" longer blade for $8 & change out the door (NAPA ain't never cheap) or make your own (better cuz you can get the gap just right). As said the center button & I like a light smear of dielectric grease on top of the rotor blade where it will contact the center button