表1-NAS 1638油液清潔度等級標准級別100ml樣品中規定顆粒大小(μm)范圍內的最大顆粒數5～1515～2525～5050～100>1000012522410025044820150089163121000178326132000356631124400071212622458000142525345861600028505069016732000570010121803286400011400202536064912800022800405072012810256000456008100144015611512000912001620028805121210240001824003240057601024 表2-ISO 4406-1987 油液清潔度等級標准顆粒數/毫升清潔度等級顆粒數/毫升清潔度等級大於上限值大於上限值80000160000241603201540000800002380160142000040000224080131000020000212040125000100002010201125005000195101013002500182.5596401300171.32.58320640160.641.37 表3-ISO 4406-1987與NAS 1638油液清潔度等級對應關系ISO4406-198721/1820/1719/1618/1517/1416/1315/12NAS16381211109876ISO4406-198714/1113/1012/911/810/79/68/5NAS163854321000。