Think / pen cap

When people are holding a pen for writing, they are likely to wrestle the pen
cap while thinking.But it is easy to break the pen cap and people have to buy
new pens after a long time of repeating this act because all pen caps are
completely stuck to pens. However, this kind of pen can solve this problem
perfectly because the pen cap is designed separately from the pen which
enables it to stretch for certain degrees.Besides, it can bring much convenience to grab books.