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"2B铅笔"的 B 是哪个单词？你肯定认识，但是猜不到 英语九点半 昨天
铅笔用石墨含量来给铅芯的硬度或者黑度分级。
A pencil lead is made from graphite mixed with clay. Graphite is a naturally soft substance and clay is mixed with it to make it harder. This means a lead with a high graphite content is known as a soft lead and pencils with a soft lead will make a dark mark when used.
铅芯是由石墨和粘土混合制成的。石墨是一种天然的软物质，人们把它和粘土混合在一起使它变硬。这意味着石墨含量高的铅被称为软铅，软铅的铅笔在使用时会留下黑色的痕迹。
Conversely, a lead with less graphite and a higher clay content is known as a hard lead and will make a lighter mark.相反，石墨少而黏土含量高的铅被称为硬铅，它留下的痕迹较浅。
软铅芯用字母B来表示它们黑的程度。然后，数字被用来表示柔软程度——数字越高，铅越软，所以画出来越黑。例如，2B铅比B铅软，会产生更黑的痕迹。4B比2B等要软。
Hard leads are graded in the same way, but use an ‘H’ to show how ‘hard’ they are. A 2H is harder than an H and a 6H is really really hard.
硬铅芯以同样的方式评级，但用H来表示它们有多硬。2H比H硬，6H非常非常硬。
HB (hard black) leads are considered to be the happy medium on the graphite scale. There are no specific industry standards that set down how black HB leads should be, so an HB pencil made by one manufacturer will not necessarily leave the same mark as an HB pencil from a different manufacturer.
硬黑铅被认为是石墨刻度上的理想中值。并没有具体的行业标准来规定HB铅笔芯应该有多黑，所以一个制造商生产的HB铅笔并不一定会和另一个制造商生产的HB铅笔留下相同的痕迹。