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Date: 30 July 2016. Bolt Sizing Primer.

(adjunct to the Moby-Cool a/c cover Installed article which should be read first)


Lots of the fellows know all this stuff and more about bolts. They learned in their daddy's shadow as he repaired items. For the neophyte this vignette offers a little bit of knowledge to get you started.

The most popular bolt used in the building of your boat is likely the 1/4 20. Pronounced quarter twenties by the old timers, that indicates the size and thread count of the bolt.

8 by 32's, 10 by 24's and 1/4 20's:


Definition of quarter 20's: 1/4" in diameter and 20 threads to the inch.

When you'd order them at a store you'd say something like "I need stainless steel quarter twenties. 2 inches long. Fifty please." You would be handed 50 of the bolts. Often with this popular size you will find it less expensive to order a box of 100. Check prices for certain.

In addition you will need nuts and washers. I prefer the larger fender washers for most applications.

Aboard Seaweed I have a large spice container filled with 1/4 20's in a variety of lengths. I keep washers and nuts in the same container. Although I would not go out and buy them (unless I got a true bargain price) I keep them in mind when yard sale shopping.

Buy Stainless Steel. The way to tell if something is a good stainless is to carry a magnet with you. If the hardware sticks to the magnet pass it by. It will rust.



Picture repeated for your convenience.

8 by 32's: A common bolt used on boats for electronics. Metric size 8 with 32 threads to the inch. Commonly called an 8 by 32. In the photograph, the three bolts on the left.

10 by 24's: A common smaller bolt used on boats. Metric size 10 with 24 threads to the inch. Commonly called an 10 by 24's. In the photograph, the two in the center.


It does take time to develop a tidy storage system for your screws, nuts and bolts. I would not buy bunches until needed. Then whatever quantity you do require, purchase a few extras. Keep them sorted into empty spice bottles. Label the top of the spice jar and you are all set the next time you need one.

I did start out with a fairly full compliment of hardware. Mine had been gathered over literally decades. Many came from our boat.

Built in 1956, she is a beauty...

Daddy built her. She is a 40' sedan cruiser with a fly-bridge.

Over sixty years one can expect to have a pretty sizable collection of hardware. Because the bolts are stainless they are still good all these many years later. Of course I have added to the collection. A girl cannot have too many stainless bolts, nuts and screws.

Just a couple days ago one of my 3/8" bolts "saved" a boat. One of these days soon I will tell you about that. I took pictures.

In the meantime, keep your Stainless hardware. Anything that sticks to a magnet can be thrown away. It is junk.

Do you have your bolts sorted or are they all in one container?
Can you guesstimate how old your oldest hardware is?

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Categories: Gear,  Vignettes,

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