[問題] 後面車架內側的孔洞？
如題。 我用的名詞還不是很正確，請見圖：
http://i.imgur.com/bFrur2I.jpg
就在橫向支架內側有兩個洞，還用橡皮釘跟皮墊堵住，想請問這目的是？
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