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Over the past few months Allied Fastenings have been asked to investigate supplying longer thread lengths on Hexagon Head Bolts or Studs and, as is common practice at Allied Fastenings, the team are specialists in obtaining accurate information in finding solutions to these queries.
Bolt length is generally measured from beneath the head of a fastener to the cut end which includes an unthreaded portion of shank (Full Diameter Shank Length) and the threaded portion (Thread Length). However, it’s important to understand the measured length of an Engineers Bolt (Bolt Length) is not necessarily the sum of the two, as there is always a small portion of thread which is not fully formed, over which a nut with a countersunk face will cover known as ‘Grip Length’.
More often than not an engineer will specify Grip Length of a fastener as they intend that the unthreaded portion of the bolt sit within the shear plane of an assembly and this is important in order to maintain integrity for the desired application.
It is important to appreciate that ISO Standards specify dimension allowances for specific nominal bolts relative to bolt length. In the case of AS1111 preferred dimensions are specified as a minimum Thread Length and a maximum Full Diameter Shank Length.
Standard Bolt Thread Lengths are described in multiples of the bolt diameter plus an allowance varying by the bolt length. The table below is from AS1111 and is a ready guide to assessing preferred thread lengths.
Nominal Bolt Length
Full Thread Length
For further detail refer: Australian Standard: ISO metric hexagon bolts and screws – Part 1: Bolts.
Allied Fastenings are specialist distrtributors of premium industrial fastenings, and their distribution channels cover the length and breadth of New Zealand, so to find out more about their products, please visit the website at http://www.alliedfastenings.co.nz