Crankshafts can also be machined out of a billet of steel. The AK-47's barrel and bolt were milled out of a steel billet and hard chromed. The silencers with billet endcaps are also black. Many tuning firms producing billet cranks misunderstand the design criteria of counterbalance weights. A breastplate is added, usually attached to the front billet. These include the escutcheon or inescutcheon, lozenge, fusil, mascle, rustre, billet, roundel, fountain, and annulet. It works by placing the billet in a heavy walled container. They supply a constant pressure throughout the whole billet. For all prospective students, an assignment in a billet requiring pathfinder skills is generally required. The grain of all veneers in the LVL billet is parallel to the long direction. Modern processes are highly controlled and include a compressive force on the billet. Container temperatures should be identical with, or only slightly higher than billet temperature. The "Einsatzgruppen" depended upon their sponsoring army commander for billet, food, and transportation. Sergeant major is both a rank and a military billet. The average tour length per one-star billet is two to four years.