In English, people often say "stuff" when they refer to things generally, you don't need to say specifically what they are.
For example, "please move your stuff (you don't need to say specifically the books, mobilephones, etc) off the table".
In Vietnamese, we often say "the gut of a pen, a mobile phone, or a machine" (translated literally from Vietnamese to English) when we want to refer to the inner part of something generally?
Do we have a similar word to generally refer to the inner part of a thing (such as a pen or a machine)?