What u have highlighted in ur pic this is not a nut sir! Its a dip stick! It is to check the engine oil level...
He changed ur shiny new, good quality one and installed his... Allah hidayat day is qoam ko? kuch paison ki khatir akhirat barbad karty hen...
Well u can easily buy a new one sasti he hogi. Better get one which comes with Honda CD70.. woh tutay gi nai zor se kasnay pe be.