How to find bolt & nut size, metric or imperial.

This is helpful information for a situation where you need to replace a piece of hardware, such as a bolt or nut, and you are unsure of the size. We'll discuss how the measurements are taken and reference, but also some quick ways and tools to check the hardware size.

Referenced video for how to determine 'Metric or Standard (SAE) Bolt':

Referenced link to thread checkers (Amazon affiliate link):

Referenced link to handy hardware bins and dividers (Amazon affiliate link):

#howto #mechanic #learning

Disclaimer: of course, this video is for entertainment purposes only........you are responsible for any and all of your own actions......not me. Disappointing we have to say things like this in today's world, but here we are. Stay curious, friends.

[richardseifert]

Hi James
I'm restoring a 1971 Datsun 240Z and these OEM bolts are head stamped from blank, 4, 7, & 9 which I took for strength ratings which you confirmed in your great Video. I know that sometimes Engineers also select fastener strength based on the how critical that system is to the safe operation of the product. On this car the rotating drive train parts use 9 head stamped bolts and the stationary supporting drive train structure uses 7 head stamped bolts. Blank and 4 head stamped bolts are used least critical and frequently removed parts. Anyway great video!! Thanks

[garymucher]

Good video with accurate information. I have a plate with both metric and SAE for bolts and nuts. But I also have the thread pitch gauge as well. Some time I use one over the other depending what I am doing. So many times metric and SAE are so close they basically look the same until you try to use one for the other. So having the gauges makes quick work of sorting them out... Thumbs Up!

[kagnewmp]

This was great and you have a new Subscriber. I have seen similar thread checkers at a much higher price so I immediately ordered from your link. Thanks a lot

[josephstratti]

Amazing thought that went into naming grades of bolts, as it has 3 lines on the bolt so that is a grade 5 bolt!

[johnkangas]

Here's something weird for you: the rear axle on my 1991 Trek 820 mountain bike is 10mm in diameter, but the thread pitch is 26 threads per inch! So, that's two different measurement systems used in a single part. I found this out the hard way when I was replacing worn bearing cones. Two sizes of cones were available: M10 with 1mm threads, and M10 with 26 tpi. I assumed that it was the former (why would anyone mix metric and English standards in the same part?). The two thread sizes are close enough that the thin lock nut that gets wedged against the bearing cone would thread onto the axle even though the nut was a 1mm thread and the axle is 26 tpi. However, the bearing cone is longer, and the error accumulates, and the cone with 1mm threads won't work on the 26 tpi axle. Why anyone would design the axle that way is beyond me.

[jagracershoestring]

You have omitted Aircraft fixed pitch series bolts, which America used to be fond of to keep spares prices high. Whitworth, Sae, Unified series for automotive use. Metric fine, medium and course. Its a minefield, and one needs a pitch gauge set, and a shadow machine to measure thread angles. And then there are Indian made with a swinging breezeblock threads! often 47 degree angle threads.

[mbergheaud]

When would someone use a coarse-threaded bolt instead of a fine-threaded bolt?

[dac]

Easy to determine based on wrench size! I have a bolt sizer but almost never need to use it.

[daveylad]

Nice video I’ve never seen those thread checker sets before, I always used a thread gauge Here is a little tip to go with metric bolts, do you know how to determine the bolt head/ spanner size for a given bolt diameter?
Bolt diameter x 1.5 +1. ( up-to 14mm iirc after that just it’s just x1.5)
8mm bolt x 1.5 = 12 +1 = 13., 13mm spanner

[johnscotland]

Can the thread checker at the end be inserted into a threaded hole?

[MattLitkeRacing]

My favorite is when someone brings me a bolt and I know it’s m8 x 30 just by looking at it

[My-Pal-Hal]

JAMES ???, what the...
Then where in the hell is Dad ?😳?
... 911 😂 🖖

[ytfan]

M8 x 1.25 is easy to measure with 4 threads, it makes 5mm, easier to see on a caliper, just like M5 x 0.8, ... 5 threads make 4mm. 😉

[jeffreyfwagner]

Heads Up Here SAE has nothing to do with nut and bolt sizes. The standard that once covered thread dimensions was called SAE J475. It has been replaced by ANSI B1.1 as of 1964. If you look in a SAE handbook you will see text telling you to use the ANSI data. There are no printed specs for screw threads in the SAE handbook.

[Smoorepainter]

It's a great think, Standardizaation...makes things so much simpler...lol! America had to brutal war with Britain...and yet they keep the Imperial System. WTF. Good video.

[hidnax]

Metric bolts _ARE_ the standard bolts. All those inch bolts are used only in usa and nowhere else