The unique design of MSD's Pro-Billet crank trigger distributors fit tight intake systems while still transferring the high voltage of the MSD racing ignition to the spark plugs. Since these distributors are used primarily in racing applications, an oversized steel shaft is responsible for delivering the sparks reliably and accurately. The shaft is QPQ-coated for friction reduction and is guided by a sealed ball-bearing assembly at the top and an extra-long sintered bushing at the bottom for smooth operation and lifelong reliability. Chevrolet models also have two O-ring grooves at the base of the housing to prevent oil in the lifter valley from leaking through the oil passage, and are available with an adjustable slip collar for tall blocks. For high rpm stability, the housings are CNC-machined from solid billet 6061-T6 aluminum that is machined to within 0.001 in. for absolute accuracy. These distributors have a low-profile Rynite cap assembly to clear busy intake setups. The low design is accomplished because the only thing under the cap is a rotor! The high voltage carrying capabilities are the result of several features, including a large diameter cap with wide spaced terminals, and an injection-molded Rynite rotor with thick vanes to stir up the air inside the cap. The high dielectric Rynite base also prevents arcing to the billet housing. They're also available in Crab Cap models to clear tunnel rams and superchargers, or with slip collars for modified blocks, heads, and intakes. These distributors don't have an advance assembly or pickup, so they must be used with a crank trigger. They also require the use of a separate ignition box, such as an MSD 6, 7, 8, or 10 Series ignition.