Questions and Answers

Down To The Nuts And Bolts Q. Hi Vince, This may or may not be an appropriate question for the Automotive section, but here goes. I'm looking for information on how nut and bolt sizes are measured, sized and sold. For instance, I just bought some 5/16" x 24 nylon lock nuts. Are these the same as 10-24 lock nuts?

What's the difference between the 5/16" designation and the "10"? Is the 10 in mm, and therefore metric? When a catalog says UNC, UNEF, etc. what's that mean? And what about all those ASTM numbers and Rockwell ratings?

I'm confused. Can you recommend a good web site for finding this out? If you search on "nuts and bolts" you get millions of hits, because "nuts and bolts" is an expression of "how-to" something. I've tried various permutations and words like measurement, comparison, metric, standard, dimensions, etc. but have been unsuccessful.

Perhaps you've stumbled across a source?
Thanks!

A. I think you'll find most of what you're looking for here:
The Drive Train Page.

There are many types of lock nuts. The two most common are the split nut type and the nylon lock nut. Lock nuts are generally used when a lock washer, for some reason, is impractical. The split type has the threads cut in such a way that they apply pressure on the threads of the bolt. This pressure locks it in place. The nylon lock nuts use a nylon insert to do the holding.

The ASTM (the American Society for Testing and Materials) sets certain standards and the ATSM number indicates which standard is met.

Generally, nuts and bolts smaller than ¼" are expressed in numbers from 12 on down in even numbers. The higher the number, the larger the diameter of the threaded portion. So a #10 bolt is larger than a #8 and so on. Now when you get down to eyeglass size screws, you get into size 0, 00, 000 and so on. The more zeros, the smaller the screw.

The Rockwell Ratings denote the hardness of the bolt material. It is usually expressed as "10 Rockwells" or "20 Rockwells". The higher the number, the harder the steel.

If you want, most Hardware Stores will give you a chart for nuts, bolts and screws as a general reference.

Additional Information provided courtesy of ALLDATA