Dumb Question About Nut/Bolt Diameters

[ericr]

can any machinist, or any informed person, tell me if the nuts/bolts for a specific size are actually small/larger than their stated size? for example a 5/8 nut on a 5/8 bolt would not fit together because they are of equal size. obviously there is some variation but is on the nut or the bolt?

[Blue-Truck-Nut]

If I understand your question correctly,
A nut or bolt is sized according to thread size, a 1/4" bolt will fit in a 1/4" hole. Now a bolts wrench size is measured from flat to flat on the hex, a common 1/4" bolt or nut takes a 7/16" wrench. In my understanding, fasteners are sized this way as a method of standardizing, a 1/4" bolt is a 1/4" bolt, it doesn't change size if it is a carriage bolt, a stove bolt, or an alen head. That's especially true in larger sizes, say a 3/4" bolt, which may use a 15/16" wrench on the bolt, and a 1" wrench on the nut, to facilitate the use of one wrench set in larger sizes.

I hope it helps, I'm definitely not an expert on the subject.

Sent from my E6810 using Tapatalk

[alexiskai]

Generally you have a few different dimensions that need to be considered:

• Bolt size: this is the diameter of the threaded portion of the bolt, in your example 5/8"
• Thread pitch: number of threads per inch (TPI); typically designated either fine or coarse; your 5/8" bolt would have either 11 TPI (coarse) or 18 (fine)
• Head size: this is the diameter of the head of the bolt, which determines the wrench size you need; typically the head size is 2-3 sizes up from the bolt size

If you have a 5/8" nut that's not fitting onto a 5/8" bolt, then either it's the wrong thread pitch or one of the two is damaged.

Here's a page showing various bolt dimensions, and here's one showing typical thread pitches.

One of the nice "easter eggs" in the Les Andrews red manual is the tables of bolt sizes. There's a table in the Engine section that gives the size, thread pitch, and head size for most of the bolts related to the engine, and there's a table at the very back of the book that gives bolt size, head size, and standard torque values for dry vs lubed and for grade 2, 5, and 8.

[abachman3]

The bolt is sized on the outside diameter. The nut is actually sized based on what size bolt fits into it... thus the diameter of thee inside threads, not the outside threads.

[alexiskai]

It's sometimes the case that a nut and bolt that have the same head size will have different diameters for the threaded portion. Or vice versa - for example it's common to see a 1/4" bolt with a 1/2" head, but the 1/4" nut that fits it has a 7/16" head.

[rotorwrench]

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Thread pitch OD will always be a bit smaller in diameter than the hole it is made to fit as is the non-threaded shank of a bolt. If you get your hands on a Decimal Equivalents and Tap Drill Sizes chart for unified type thread then it will give a person the size of hole to drill in order to get the correct pitch of threads tapped into it.

In aviation, there are several classifications of fastener fits. There are normal fits and close tolerance fits. If the bolt hole is exactly 0.25" in diameter then the bolt will have to be smaller in shank diameter to fit. A close tolerance bolt with be manufactured to a tolerance of within several ten thousandths of a smaller diameter. The diameter would be 0.2495" to 0.2485 . A standard fit for automotive could vary as much as three to four thousandths. Many bolts are plated and the plating has to be within a tolerance as well or the bolt could be too tight to fit the bore of the bolt hole.

There are also classifications of thread fit but it depends on what type of thread is being utilized and what tooling is available.

[David R.]

Machinery handbook gives industry standards for the tolerances

[GPierce]

https://www.boltdepot.com/fastener-i...rill-size.aspx

[Big hammer]

Originally Posted by ericr

can any machinist, or any informed person, tell me if the nuts/bolts for a specific size are actually small/larger than their stated size? for example a 5/8 nut on a 5/8 bolt would not fit together because they are of equal size. obviously there is some variation but is on the nut or the bolt?

Are you asking about the fitting of the nut to bolt, I believe this is called thread class, like the close fitting bolts in the rearend as compared to a hardware store bolt.

[ericr]

Originally Posted by Big hammer

Are you asking about the fitting of the nut to bolt, I believe this is called thread class, like the close fitting bolts in the rearend as compared to a hardware store bolt.

-I don't know exactly what I meant. I ask because I try to install battery tenders such that the negative lead is fastened underneath the nut on the starter switch, which is a 5/8 nut. I never like using the squeeze clamps for fear they would fall off if the cat played with the wires.

[alexiskai]

Originally Posted by ericr

-I don't know exactly what I meant. I ask because I try to install battery tenders such that the negative lead is fastened underneath the nut on the starter switch, which is a 5/8 nut. I never like using the squeeze clamps for fear they would fall off if the cat played with the wires.

In this case, 5/8" is the head size; the "nut size" is 3/8"-16, so you'd need a 3/8 or M10 ring terminal for the tender.

[alexiskai]

Here's my battery tender arrangement

[ericr]

gee, you have a better location for the positive terminal...I had been attaching it though the little machine screw that holds the wiring harness in place near the side water outlet

[Jack Shaft]

Took a fastener class at the Caterpillar dealer when I worked field service.Amazing class on design,composition,treating processes and applications. Caterpillar was on the cutting edge of fastener locking techniques and anaerobic sealants..consistency in fastener manufacturing and design allowed the torque value of the fastener properly supported to lock the assembly and negate the use of locking hardware.

[woofa.express]

hello ericr.
I can't answer your question simply because I do not know. So if you think you are dumb you had better count me in too.
I left school 55 years ago. A teacher who I respect told my class the following.

"don't be afraid to ask what you don't understand. For if you don't understand you can bet others in the class don't either".

I worked in Malaysia for quite some time. If you asked any of them a question they felt obligated to answer even if they didn't know. I'd go to work each day and give them this little lecture- If you don't know the answer to my questions say "I don't know". I repeated that little statement following any question I asked at any time.

[alexiskai]

Originally Posted by ericr

gee, you have a better location for the positive terminal...I had been attaching it though the little machine screw that holds the wiring harness in place near the side water outlet

I had actually been doing that too, but when I added the ground cable at the starter bolt, visible in the picture, it seemed to me that the grounding pathway from the starter switch to the starter to the battery was now at least as good as, if not better than, the path from the cutout wire clip to the engine block to the chassis to the battery. And obviously the wiring is tidier.

[Terry, NJ]

After a lifetime of messing around with bolts, threads, and screws ( I am the only person I know who collects odd size taps) Nominal bolt sizes will mike what ever the size is. Say 1/2X13 will mike .498/499, some will actually mike .500. The tap will mike .505. This why I save broken taps, the shanks are .005 larger than the nominal size. Comes in handy now and then! To make a nut, an undersize hole is drilled. This leaves the "meat" on the nut to cut the thread. The hole or "tap drill" size for a 1/2 " nut is 27/64 or about .421. This will give you a 75% thread. For a greater percentage of thread, simply use smaller tap drills. Ford used a tighter (smaller) hole and a slightly larger bolt size which is why we don't "chase" threads with a tap or die. Chasing threads with today's equipment enlarges them and destroys the original close fit. Although, I do chase bolt threads with an adjustable die opened up most of the way. There now you know more than you ever wanted to know about threads. Terry

[jimalabam]

ericr: There are no dumb questions, If you do not know the answer...