Bolt / Nut sizes

Thu Jan 27, 2005 8:16 am

Here's some rather generic questions:

When working with bolts, is there basically just three things to consider; length, diameter and thread pitch? Say if I have a bolt and I need a replacement, the length is a no brainer.

Thread pitch: Should I be able to use a pitch gauge to get virtually any tpi? I see in the MSC catalog where they have an sae pitch gauge that has 12 templates, going from 8 to 28 tpi. Will I ever find any thing in between these or are these all I should ever run across? Is metric threads per centimeter? I see they also have metric gauge.

And as far as diameter, Can I just measure the out side of the bolt to get this? In which case measuring the inside of a nut would give me an erroneous measurement...


Thu Jan 27, 2005 8:57 am

It has been my experience that only on rare circumstances will there be an oddball tpi. There are different tpi for metric. As for the bolt diameter, the shank of the boly is the dia. You can get a bolt gauge for diameter pretty cheap, which does make it easier.

Thu Jan 27, 2005 9:18 am

Don't forget the hardness that's stamped on the head of the bolt. Someone else can give the different strengths and markings. I don't have my book in front of me.
Last edited by Rick Prentice on Fri Jan 28, 2005 7:54 am, edited 1 time in total.

Thu Jan 27, 2005 10:17 am

You can run into non-standard threads in odd places. On a Cub most threads will be standard coarse threads for the given size and most bolts will be grade 5. There are exceptions to both. For the basic descriptions and identification look at these pages:


Coarse threads:

Fine threads:

Thu Jan 27, 2005 11:11 am

This whole list of stuff is good:

Thanks Jim. Maybe this could be added to the links page.(?)


Fri Jan 28, 2005 5:24 am

Stanley woodworking planes use off beat tpi. They have been manufacturing metallic and transition planes since about 1866 and plane collecting has evolved into a significant hobby with thousands of collectors world wide. Plus there are thousands of users who prefer the older "user friendly" planes. Stanley was clever in using non standard threads for the various bolts in their planes which captivated a portion of the market by requiring a customer to return to them for a bolt. Further, it has created a market for clunker Stanley planes for the purpose of salvaging parts, especially bolts.

Fri Jan 28, 2005 11:40 am

Wow, I normally can judge the size of a bolt just by looking at it, and whether it's a fine or coarse thread... Never occurred to me that if you haven't been around bolts your whole life, you wouldn't be able to do that.