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Odd bolt size

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AdrianR31/03/2019 12:19:24
136 forum posts
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I have just bought a cheep ebay engine hoist and the bolts that hold the castors on are M8. The odd thing is the head and nuts are 14mm across the flats.

I am pretty sure they are metric as they have specification 8.8 on the heads.

Googling bolt dimensions says they should be 13mm.

Anyone have any idea why they are 14mm?

Hopper31/03/2019 12:39:31
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Various cars and motorcycles use 14mm heads on bolts and matching nuts. No idea why. I have had to buy a 14mm socket or spanner to complement a set that came without it more than once over the years.

There seem to be various standards of metric, ISO, ANSI, DIN and a Japanese one. And Chinese manufacturers seem to have a pretty freeform approach to such things. They may have their own standards but they exist out of sight on the other side of the language barrier.

 

 

Edited By Hopper on 31/03/2019 12:45:57

JasonB31/03/2019 13:18:48
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14mm on M8 is quite common but don't know why, maybe so all the old fogeys with 9/16 spanners like that size

Nicholas Wheeler 131/03/2019 13:31:00
228 forum posts
13 photos
Posted by AdrianR on 31/03/2019 12:19:24:

I have just bought a cheep ebay engine hoist and the bolts that hold the castors on are M8. The odd thing is the head and nuts are 14mm across the flats.

I am pretty sure they are metric as they have specification 8.8 on the heads.

Googling bolt dimensions says they should be 13mm.

Anyone have any idea why they are 14mm?

You've never worked on Japanese cars then?

Bazyle31/03/2019 13:31:17
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4485 forum posts
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the 8.8 is a strength designation. The reason for having different sized nuts is because a normal spanner set does not include two 13mm spanners. So if you want a spanner at each end to tighten it it is extremely helpful to have different sizes. The same is found occasionally in imperial bolts on cars that have been designed by someone who actually does his own servicing.

Michael Gilligan31/03/2019 13:57:18
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Posted by JasonB on 31/03/2019 13:18:48:

14mm on M8 is quite common but don't know why ...

.

... it lets them get away with using bigger clearance holes devil

MichaelG.

not done it yet31/03/2019 14:53:18
2811 forum posts
11 photos

The sensible reason for the bolt head being a different size to the nut is so that only one set of spanners need be used for maintenance. Nuts usually get damaged, so replaced more often than the bolt, so they are the standard size and the bolt head is sensibly one size larger.

JasonB31/03/2019 15:01:28
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I've got some 14mm M8 nuts so that rules out just the bolts being bigger.

Seem to remember one item I bought had four M8 flange nuts - two were 13mm and two 14mm and they fitted onto studs so only one spanner neededcrook

AdrianR31/03/2019 16:38:12
136 forum posts
3 photos

The reason i noticed it was that i am in the middle of relocating and of course my 14mm spanner is at my other place 160 miles away. At least screw fix have some cheep spanners.

Will be great when the workshop build is finished and I can move it all.

alan lloyd 331/03/2019 19:52:50
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150 forum posts

the head size was reduced way back in the 70s maybe 60s to save metal, what you have was probably made on old presses, spanners were 10x14 now I think 10x13 is more common

vintage engineer31/03/2019 20:31:43
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114 forum posts

If you want odd bolts, try working on pre-war French cars! They made up their own sizes and pitches!

Neil Wyatt31/03/2019 22:11:01
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Posted by Bazyle on 31/03/2019 13:31:17:

the 8.8 is a strength designation. The reason for having different sized nuts is because a normal spanner set does not include two 13mm spanners. So if you want a spanner at each end to tighten it it is extremely helpful to have different sizes. The same is found occasionally in imperial bolts on cars that have been designed by someone who actually does his own servicing.

Back in the 70s/80s Ford perfected this approach to the extent that you could undo all four bolts on a typical part simultaneously because they all had different heads...

Neil

Michael Gilligan31/03/2019 23:34:34
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Posted by Neil Wyatt on 31/03/2019 22:11:01:

... to the extent that you could undo all four bolts on a typical part simultaneously ...

.

Assuming that you were quadridextrous angel

... one-man-band ?

MichaelG.

Edited By Michael Gilligan on 31/03/2019 23:36:41

clogs01/04/2019 06:18:23
450 forum posts
12 photos

repaired a Chinese motor scooter no so long ago and quite a few of the nuts and bolts had 5 corners around the engine and ancilleries.....

standard threads tho.....everything got replaced with Stainess..

had fun getting the seized fixings undone......hahaha.........well funny now........

Nicholas Farr01/04/2019 06:31:07
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1807 forum posts
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Hi 13mm for an 8mm bolt is only a standard. I've seen 8mm bolts with 14mm heads a number of times and I've even come across them with a 12mm heads. Other standard sizes also have variables, like 12mm with 18mm heads, 10mm with 16mm heads. It is often due to their usage for a manufacture to which size heads are used and often down to cost if you produce equipment using many thousands of bolts per year.

Regards Nick.

vintage engineer01/04/2019 17:39:07
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114 forum posts

Modern French cars are doing this to stop no dealer mechanics working on them!

Posted by clogs on 01/04/2019 06:18:23:

repaired a Chinese motor scooter no so long ago and quite a few of the nuts and bolts had 5 corners around the engine and ancilleries.....

standard threads tho.....everything got replaced with Stainess..

had fun getting the seized fixings undone......hahaha.........well funny now........

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