Bolts & Set Screws - Guide To Threads, Diameters & Lengths

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At Stanton Marine we stock a wide variety of threaded fasteners.  All of our threaded fasteners are standard metric (which means the metric coarse thread).  In general when you buy metric nuts and bolts they are of the coarse thread unless otherwise stated, and they suit the vast majority of applications.
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The ‘bolts’ that we stock are actually set-screws.  The terms set screw means that the shank or shaft of the bolt is threaded along its entire length, whereas strictly the term bolt refers to only partially threaded.  The reason that we stock set-screws is that we feel they are more versatile and that this is less chance of selecting items that don’t fit properly.

The diameter, eg M3,M4,M5 etc. means that outside diameter of the set-screw or bolt, and also the hole which it will fit through.  Set-screw and bolts are manufactured so that they will always fit through a hole of their nominal size, so if you us a 6mm drill an M6 bolt or set-screw will fit through it as they are manufactured slightly under-size eg 5.8mm for an M6 bolt.

All of our nuts, bolts, washers and screws are A4 grade, sometimes called Marine grade.  See our separate guide for a description for the difference between A4 and A2 stainless steel grades.

The lengths of our set-screws are designated in the standard way, the definition of length is slightly different depending on whether they are hex-head or countersunk, please see the diagram below to clarify.  The main thing to not with regard to length is that for countersunk bolts or set-screws the length measurement includes the head, and for other types the length measurement is to the underneath of the head.

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