dr bob

Problem: Reading a series of posts on a mechanical fix, I found myself translating bolt sizes on my feeble brain. Since there are no 13mm bolts on the car, the issue jumped out at me. So here's a thought: When you are describing a bolt size, remember that it's the diameter of the shank on the bolt that describes the size, not the size of the wrench you used to turn the bolt or nut. So the 13mm bolt that was described in the procedure was much more likley to be 8mm, with a 13mm hex head on it. This maybe a little picky, but consider that when looking at torque specs for specific bolts, they may not all be listed; you may end up at the "all others" category, and having the wrong size based on the hex wrench used can lead to serious problems. Consider the 6mm capscrews used to hold the water pump to the alumnum engine block. About 7 lbs/ft needed on them. If you mistakenly read those as 10mm bolts from the hex head size, the "all others" torque spec is something around 35 lbs/ft. Broken water pump bolts and pulled threads would be the result.

Conclusion: It's OK to use the hex head size to describe a bolt or nut, but add the word "wrench" or "hex head" to the description when you do. Where possible, use the correct bolt size based on shank diameter though.


[/Soapbox Mode]

Ed Scherer

Good post.

While we're at it,

<CONTROVERSIAL>
we should join the rest of the world and use SI units everywhere and junk the damn U.S. stuff.
</CONTROVERSIAL>

I.e., use N·m, not lb.·ft. for torques, etc.

Minimally, always show units when a number is shown.


It probably wouldn't hurt to include lube/sealant/anti-seize/thread-lock/etc. recommendation with each reference to a fastener used in a particular application, too.

blown 87

You and I both know that just using the diameter and grip length does not tell much about a bolt.
Just how big it is.

F451

Good post. Going on 50 years old soon, and I recently decided to get with the program concerning correctly understanding fastener types, sizes, materials, applications, etc.

Amazing what a little clarity can bring to the situation, I'm finding. -Ed

TAREK

+1

even more useful, if you know the shank size, to use the "M" prefix. For example M6 nut, which on our cars, requires a 10 mmm wrench for all applications that I've seen so far.

borland

In the WSM, Vol 1, on the 32-Valve Engine Tightening table, it lists torque specifications in different formats:

70 (52)
25 to 30 ( 18 to 22 )
20 + 2 ( 15 + 1 )

some as: Nm (ftlbs), others as: Nm (kpm)

dr bob

The torque wrench numbers need to reflect the wrench you are using. The scale on the fronts of mine are lbs/ft, including the numbers on the ring, while the NM values are on the backside. I've gone through my tech-***** book and added lbs/ft values to the numbers that are not already converted. Maybe that's a step back, but it is what works with the tools I have in the garage.

dr bob

The reference that caught my eye was a picture and descrption of removing a 13mm bolt as part of a disassembly. No sealer required for disassembly, I suspect.

I was trying to remind folks to use the standard descriptions for bolt sizes to manage some of the (my) confusion. Not trying write an assembly guide, just looking for repeatbility/consistency in our descriptions.

jon928se

Being picky, but with the exception of gallons/quarts/pints the "US" measurements are Imperial - ie English.

I like ftlbs for Torque. It's a unit of measurement I can relate to on a Human scale. Whereas a Nm to my Structural engineering brain is just a very small bending moment on a beam, me being more used to kNm.

I have the same issues here in Orstrilya. Engineers here use kPa and Mpa for uniform loading on floors but kN for point loads - loading on floors should be kN/m2 because the load derives from a force per square meter not from a pressure exerted by a gas or liquid. FWIW using imperial units for floor loading also makes sense on a human scale ie 20lbs/ft2 for residential 80lbs/ft2 for office.

Or foundation loadings - 100kN/m2 = approx 1Ton/ft2 - a measurement one can relate to on a human scale.

Rant over.

Ed Scherer

I didn't want to be rude and try to pin the blame on anyone outside of my country. But, yeah, now that you've admitted it, yes, it was you guys who screwed things up. And maybe by "U.S.," I meant "unnecessarily screwy."

FWIW, I can't really relate that well to some of the SI units, either, but I'm pretty sure it's more due to lack of familiarity. I know that volumetric measurements here are a crock: fluid ounces (must be careful not to confuse with the "mass" ounce!), cups, pints, quarts, gallons, oh... and let's not forget teaspoons and tablespoons. And that there are U.S. and Imperial variants of many of those units. Holy crap, just tell me mL or L and be done with it!

Well, I did say it's controversial. We might be be arguing about this for a fortnight! Dueling at 1/20 of a furlong!

I'm so worked up about it, I'm going to go tip a pint ... um, I mean a 0.5 L.

Tails

Jon in Oz,
To further complicate the matter US gallons are not imperial gallons, an imperial gallon is 1.20095 US gallon.
Tails 1990 928S4 auto

Mike LaBranche

Raises hand... I'm guilty of said sin. As in all you need is a 13mm to fix most of a 928.
Trouble is... M8x1.5 just doesn't flow.

blown 87

No, but M8x1.5x30 8.8 tells me something.

RFJ

OMG, I'm confused

Ed Scherer

And it's a hell of a lot more uniform, compact, and easily comparable (to other sizes) notation, e.g., than 5/16"x18x1¼" 8.8 (What's next size down? 1/4". After that? #10. Total B.S., IMHO).