Measuring device for determining a thread length of a fastener

A measuring device adapted for determining a safety thread length LS of a fastener required for fastening a wheel onto a wheel hub unit, the wheel being formed with a bolt hole which extends through inner and outer major surfaces thereof, the outer major surface having an enlarged hole larger in diameter than the bolt hole so as to define a circumferential abutment seat which extends toward the inner major surface to terminate at an inner seat end that is distant from the inner major surface by a first axial length L1, said measuring device comprising:

• an elongated measuring rod which extends straight in a longitudinal direction to terminate at front and rear ends, and which has a first segment measured from said front end and set equal in length to the first axial length, and a second segment that extends from said first segment;
• a positioning member secured to said front end and configured to mate with the circumferential abutment seat such that, once said positioning member is brought to abut against the circumferential abutment seat, said second segment is rendered to be measured from the inner major surface;
• and
• a plurality of modular sleeves, each having a second axial length L2, and each configured to be sleevably positioned on and matched up with said second segment such that the safety thread length LS is determined by an equation:
• LS≧L1+L2.