BoltDepot has a great selection of charts used to identify and explain the wide variety of screws, bolts, nuts, washers and other pieces used for building just about every project you can imagine. Wood screws, machine screws, carriage bolts, lag bolts, square heads, torx, ogee washers and more.
There’s even a section about the grade/strength types of the different materials used for the fasteners. Very handy indeed.
There are several different locations on a fastener where one can measure the diameter.
The most commonly used diameters are:
- Thread Diameter (T). Also called major diameter.
- Shank Diameter (S).
- Root Diameter (R). Also called minor diameter.
Nuts and Washers
Both nuts and washers are sized by the fastener they fit. For example a 1/2 inch nut fits a 1/2 inch bolt and a 1/2 inch washer fits the same bolt.
Note: When purchasing nuts the Thread Count or Pitch must also match that of the bolt. For more information please see our About Thread Pitch and TPI page and or How Fastener Measurements are Notated page.
The diameter of a hex bolt is the Shank diameter, expressed in inches for US bolts and Millimeters for Metric Bolts. Because this is approximately the same as the Major or Thread diameter the thread diameter measurement can be used for fully threaded bolts.
Machine screws are measured in the same way as hex bolts above.
US machine screws under 1/4 inch are then cross referenced to a size number. See our US Machine Screw Diameter Table.
Socket Head Screws
Socket head screw diameter is measured in the same way as machine screws.
Carriage bolt diameter is measured in the same way as hex bolts.
Lag bolt diameter is measured in the same way as hex bolts.
Thread diameter is used when measuring wood screws. The measurement is then cross referenced to a size number. See our Wood Screw Diameter Table.
Sheet Metal Screws
Thread diameter is used when measuring sheet metal screws. The measurement is then cross referenced to a size number. See our Sheet Metal Screw Diameter Table.
Only the shoulder diameter is used when measuring shoulder bolts.
Hit up boltdepot.com and get your next project planned out correctly. Good stuff!
Also: don’t forget about the $38 (and free shipping) Leatherman Skeletool offer on Amazon. I love that one — still can’t believe how cheap they’re selling it.