One of those old farts cornered me and I couldn’t make a run for it.

However, he gave me a great piece of information that I would like to share.

How to figure out the wrench size of a bolt from the thread diameter.

Metric: Multiply the diameter of the threaded part of the bolt by 1.5 and add 1mm
Ex. 6mm bolt x 1.5 + 1mm = 10mm wrench

Standard: Multiply the diameter of the threaded part of the bolt by 1.5 and add 1/8
Ex. 3/8 bolt x 1.5 + 1/8 = 3/4in wrench

Thats cool.................first time I ever heard that before.

__________________
Proud owner of ....
1971 280SE W108
1979 300SD W116
1983 300D W123
1975 Ironhead Sportster chopper
1987 GMC 3/4 ton 4X4 Diesel
1989 Honda Civic (Heavily modified)
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Section 609 MVAC Certified
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"He who fights with monsters might take care lest he thereby become a monster. And if you gaze for long into an abyss, the abyss gazes also into you." - Friedrich Nietzsche

Because the formula doesn't seem to work for standard bolts.

Examples - a 1/4 inch bolt takes a 7/16 wrench. The formula listed would tell you to use a 1/2 inch wrench.


A 3/8 bolt takes a 9/16 wrench, not a 3/4 inch wrench as you have listed. By the formula, a 3/8 bolt would need an 11/16 wrench, not exactly 3/4.

So much for free advice.

SteveM.

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'93 190E/D 2.5 Turbodiesel 5-speed (daily driver)
'87 190D 2.5 Turbo rustbucket - parts car
'84 Dodge Rampage diesel - Land Speed Record Holder
'13 Ram 2500 Diesel
'05 Toyota 4Runner

I think your arithmetic in your second example is flawed.

Aside from that, have you checked this guy's suggestion to see how often it comes up with the right answer?

(Edited to add: I see that Jetmugg has already pointed both of these out!)

I haven't verified that what they present is correct, but you might look at these charts for metric and fractional inch information.

Hey wait a minute!
What exactly constitutes an "old fart"?

__________________
Think Alternative Energy!
300CD '80 (now gone but not forgotten...)

This old fart has noticed 8mm bolts are most often 13mm across the flats.
So: 8mm x 1.5 = 12mm. Plus 1mm = 13mm.

That sure works on German tin but the Japanese use 8mm bolts that are 12mm between the flats.

So, by the formula>>>>> 10mm X 1.5 = 15mm. Plus 1mm = 16mm.

Oops. most 10mm bolts are either 15mm or 17mm (most common) between the flats.

Hunt the old fart down and inform him that his dog won't hunt.

__________________
You can get farther with a smile and a gun than you can with just a smile.

1984 300D
1985 300CD
1980 300SD
1993 SL500

Well its too late for any serious thought......but I guess you guys explained why I haven't heard that one before....becasue it doesn't work.

__________________
Proud owner of ....
1971 280SE W108
1979 300SD W116
1983 300D W123
1975 Ironhead Sportster chopper
1987 GMC 3/4 ton 4X4 Diesel
1989 Honda Civic (Heavily modified)
---------------------
Section 609 MVAC Certified
---------------------
"He who fights with monsters might take care lest he thereby become a monster. And if you gaze for long into an abyss, the abyss gazes also into you." - Friedrich Nietzsche

Remember today because sooner than you think YOU will be the old fart.

__________________
1999 E300 TurboDiesel
2007 Ford Explorer limited
1981 John Deere 650 Diesel tractor

I'm 43.........to some people I am an old fart already.

__________________
Proud owner of ....
1971 280SE W108
1979 300SD W116
1983 300D W123
1975 Ironhead Sportster chopper
1987 GMC 3/4 ton 4X4 Diesel
1989 Honda Civic (Heavily modified)
---------------------
Section 609 MVAC Certified
---------------------
"He who fights with monsters might take care lest he thereby become a monster. And if you gaze for long into an abyss, the abyss gazes also into you." - Friedrich Nietzsche

thats funny
I didn't think to even test what he told me or check the math
I made the age old mistake of beliving a crapsman.

Yeeeesh..........

I'm 46 with 3 kids and 1.5 Grandkids...........

Just broke my left wrist snowmobiling trying to stay young.

So much for wrenching on the MB for a little while.

Stephen (aka Snuzzy Tumblelina)

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98 K2500 Suburban 6.5 Luxo Barge

"We cannot change the wind - But we can adjust our sails"

Here is another formula for you:

If the difference between 2 numbers is one, the difference between what you get when you put them side by side and then reversing the order is 9

12 and 21
23 and 32
34 and 43

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99 E300 Turbodiesel
91 Vette with 383 motor
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04 Tailgator 21 ft Toy Hauler
11 Harley Davidson 883 SuperLow

I may be wrong but wouldn't it be easier to use a caliper to determine the size of nuts and bolts? I am a maintenance mechanic in an alumina plant and come across all kinds of nuts and bolts. I have found out over the years that a caliper in my back pocket will save a lot of trip to the tool box.

This advice from an 'old fart' of 62.

I have a question.

If you have a bolt in one hand and a ruler in the other what part of the bolt are you going to measure to see what size wrench it takes??

Danny

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1984 300SD Turbo Diesel 150,000 miles

OBK member #23

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The head across the flats...

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