Crankshafts are usually made from metal, with most modern crankshafts being constructed using forged steel. Special connecting rods, crankshafts, and pistons were fitted as well as a custom exhaust. Complex models such as engines are composed of individually designed components, e.g. pistons/crankshafts. Some high performance crankshafts also use heavy-metal counterweights to make the crankshaft more compact. The new company manufactures axles, driveline systems, chassis systems, crankshafts and chassis components. BFL's products include front axle beams, steering knuckles, connecting rods and crankshafts. A typical example is counterweights on crankshafts in piston engines. The F136 engines had crankshafts that were machined incorrectly. All 425 engines were fitted with forged steel crankshafts with harmonic balancers. The eccentric shafts do not have the stress related contours of crankshafts. Forged steel crankshafts, and cast iron main bearing support girdles became standard with the 3VZ-FE. The F136 engines had incorrectly mounted crankshafts. Some high performance crankshafts, billet crankshafts in particular, use nitridization instead. Flat-plane crankshafts were used on several early V8 engines. The most common construction methods for crankshafts are forging (usually through roll forging) or casting.