管狀物件，帶或不帶凸緣，旨在減少摩擦，並在平行於孔軸線的表面上承載動載荷。必須具有可見或可檢測的潤滑裝置，或可自潤滑。總長度必須超過外徑的25%或本體週邊平面之間的最短距離，但直管狀（無凸緣或肩部）物體除外，其承載面僅平行於孔軸線。包括分成兩段或多段，且承載圓週角不超過180度（3.141弧度）的物件。另請參閱襯套、套筒；墊片、套筒；以及墊圈（經修改）。不含：銷、空心。
items are being coded as critical to insure source inspection will be performed at the point of manufacture, prior to material receipt by the us navy or other dod components. these items are piece parts or end items in support of vital military hardware necessary to sustain the successful mission of the ships, submarines, and shore stations of the us navy. critical features including, but not limited to, dimensions, tolerances/clearances, electronic characteristics, and metallurgical properties will bespecified for government q ar (quality assurance representatives) to insure the highest possible degree of quality and reliability of these parts being delivered under navicp contracts special features, feat criticality code justification
