The utility model discloses a detection instrument for expanding disconnected formula connecting rod fracture width, the bloated detection of breaking the bloated fracture width of having no progeny of formula connecting rod of mainly used engine. Its main technical scheme: at base along central line left part, through locating pin and bolt installation major part hole location stem stem, it has agroove to open on the base, and each division of symmetry has a sulculus around the stem stem of major part hole location, at base along central line right part, and interference fit installation microcephaly hole location stem stem. The utility model discloses application proof: fundamentally - has overcome former detection mode and has detected accuracy, complex operation's phenomenon inadequately, reaches the accuracy that ensures the testing result effectively, improves detection efficiency, satisfies the disconnected formula connecting rod mass production's that expands demand.