Body

Identifying Your Fastener

Identify the type of fastener, i.e. Set screw (1) / Bolt (2) / Allen Screw (3) / Countersunk (4) / Pan Head (5) / Round Head (6). (See Fig 1 below).
Measure the diameter of the shank of the bolt with accurate Vernier Caliper / Micrometer (Fig 2).
Measure the length of the shank using Vernier / Engineers Steel Rule, see Fig 2. (Do not include the length of the head except when measuring countersunk fasteners). In the example above the size is 1 1/2" x 1/4".

WHEN ORDERING FASTENERS ALWAYS USE THE ABOVE MEASUREMENTS - NEVER REFER TO THE HEAD OR SPANNER SIZE.
Use an Engineers Steel Rule or Thread Gauge to measure the number of threads per inch (TPI) (Fig 3).
...Or to identify Metric fasteners either use a Thread pitch Gauge or Engineers Steel Rule to measure the distance between 10 threads. E.g.: In the example above 10 threads have a length of 2.0 CM, therefore the pitch is 2.0. (Fig 3).
Use Fig 4 Below to identify the thread type for Metric & Imperial thread Pitches.

Diameter (Metric) M3 M4 M5 M6 M8 M10 M12

Pitch 0.50 0.70 0.80 1.00 1.25 1.50 1.75

Diameter (Metric)	M3	M4	M5	M6	M8	M10	M12
Pitch	0.50	0.70	0.80	1.00	1.25	1.50	1.75