Smallest/Largest Bolt/Nut Automotive?

[YoshiMoshi3]

So I was wondering what's the largest and smallest bolt/nut you have come across in passenger vehicles. As far as diameter of the bolt head or nut. What application where they used in?

I think axle nuts tend to be rather large, but am not sure if there's larger bolts used elsewhere? I think some interior fasteners that are small as well?

I have never come across anything smaller than 10 mm. Are there axle nuts larger than 36 mm for passenger vehicles? I know sizes less than 10 mm and greater than 36 mm exist, I'm just wondering what application and for what vehicles.

I'm just wondering here. There are some sizes less than 10 mm that I'm missing for sockets. I was thinking of getting an axle nut socket for my car (mine is 30 mm 12 point). I was looking at some axle nut sockets online, and I can get a set of 4-5 for about the cost to buy two individually. I can always just buy as I need them, but if set is about the cost of two, then I'm pondering just buying the set. If sizes greater than lug nuts aren't used typically for anything other than axle nuts, then it might just be a waste of money though and I should just buy what I need for now and accept that I'll be missing sizes that I have no use for.

 

[Dave455]

Axle nut’s are typically the largest you will find on most vehicles. Definitely worth getting a socket this size. Mine are 46mm and I can’t think of anything bigger on my vehicle.

Bear in mind that beyond about 19mm, there are some sizes that are never used, and some that only exist in obsolete standards. In metric I regularly use 22, 24, 27, 30, 32 and 36. I own a few more, but can’t remember the last time I used them.

It’s definitely worth getting the sizes your own vehicle uses. I pretty much guarantee you will need them for other things too.

Sizes smaller than 10mm abound. 8mm and 7mm are the standard ISO (and DIN) nut sizes for 5mm and 4mm bolts respectively, so these are common. I need 8mm for much of the plastic trim on my vehicle.

7mm is also a standard hose clip size, as is 6mm, so these are also common. 5.5 is the standard size for 3mm bolts.

Although the smaller sizes are rare, you do sometimes find them on electrical terminals.

Personally, even in my “road box” which is as minimal as I can get it, I have sockets of 5.5, 6, 7, 8, 9, and 10, and have used them all (although the 9 is very rare).

 

[YoshiMoshi3]

Hey thanks! Which vehicle used a 46mm axle nut? Seems large, but good to know some vehicles use them that size.

 

[mike93lx]

I believe some bmw's use a 46mm axle nut

My Flex is "only" 36mm

Something like 4.5mm is the smallest I think I've seen on anything modern

 

[KnurledNut]

IIRC, Land Rover has a 2-1/16 ? hub nut.
Several different size lock nut sockets for trucks, 55mm, 2-3/8, 2-1/2, and other 8 points but cheap stamped sockets can be bought for these applications.
1-11/16 on some Dodge HD hub nuts.
39mm on some Toyota hub nuts.
46mm on some BMW spindle nuts.
64/65? 12pt on some BMW pinion nuts, but a special factory tool is best used.

 

[Dave455]

Hey thanks! Which vehicle used a 46mm axle nut? Seems large, but good to know some vehicles use them that size.

My BMW, and many others, use 46mm.

You can get dedicated hub nut sockets, which are a bit lighter / cheaper than some, but I have a 3/4 drive socket set, so no problem!

The same BMW uses 36mm for the oil filter. Again, you can get dedicated “oil filter” sockets, but if you have regular sockets in the appropriate sizes, you are always covered!

Generally speaking, if I need a tool once, I buy it - especially if it’s something multi purpose like a socket. I have never regretted this policy!

 

[YoshiMoshi3]

Are oil filter sockets strong enough for bolts and nuts? Example can you use a 36 mm oil filter socket on a 36 mm bolt?

 

[M6erfan]

Are oil filter sockets strong enough for bolts and nuts? Example can you use a 36 mm oil filter socket on a 36 mm bolt?

Oil filter caps are low torque fasteners and their sockets are pretty light weight/duty. Axel nuts not so much. So no, typically not.

 

[Dave455]

Are oil filter sockets strong enough for bolts and nuts? Example can you use a 36 mm oil filter socket on a 36 mm bolt?

You probably could, if the torque was low, but the dedicated oil filter sockets I’ve seen are very low profile, and wouldn’t engage properly on a nut or bolt head.

A proper 36mm socket, will of course do all tasks!

 

[richfinn]

5.5mm smallest and 41mm largest, these actual hex sizes are the wildest extremes I've come across in 35 years working on vehicles (very rare).

 

[macs_rock]

Ford Crown Vic head light adjusters are 4.5 or 5.5mm IIRC. The only set the parts store had that went that small was a set of "ignition wrenches" which I imagine are for distributor components, but I've only had to work on more modern stuff.

 

[Tool Using Animal]

Definitely get sizes 30 and above in 12 point, because sometimes axle nuts are 12 point, and at that size, you're not going to round off any hex nuts even with a 12 point socket.

 

[engineer2]

I'm sure if you got into the onboard electronics, you'd find some very small fasteners. Not a common thing to tear into.
The largest by far is the nut behind the wheel.

 

[BarrelRoll]

Pinion nuts get up to 1 7/8" sized depending on the pickup and many Jeeps use 1 5/16" sized pinion nuts.

CJ/ Scout Dana 30/ Dana 44 use 2 1/16" wheel bearing hub nuts.

 

[sparky 1971]

I used to have a 1984 Oldsmobile something or other. Small four door car with a 4 cylinder. I don't remember what is was for (I know it wasn't axle related) but I do remember having to make an hour and a half round trip to Sears to get a 32mm wrench. I still have the wrench and it still has the sku sticker on it because it hasn't been used since.

EDIT: I got on a roll and left out that the largest I've used so far automotive wise is a 38mm for the axle nuts on my Jeep Commander.

 

[2ndGearRubber]

Largest I see with ANY regularity are the 43?mm dodge 4WD truck axle nut, and the 38mm toyota axle nut. Some axle nuts on euros are bigger, and you'll run into 44mm and similar on transfer case/diff nuts.

Outside of axle nuts, it's rare to be going above 24mm or so. There just aren't that many connections made with hardware large enough to require it. A 32mm or similar axle nut is on an M20/M22 sized axle, right? So think about the rest of the car, and what parts can facilitate a 20mm fastener within them. You're not holding caliper brackets, crank bolts, or struts in with stuff that large.

 

[DAustin]

VW Bug axle nut 36mm, and old VW Bus axle nut 46mm.

 

[Jweebothee]

Smallest I have run in to on my Corolla is an 8mm nut on the alternator that needs a very thin wrench, I didn’t realize until I had to replace it, lucky for me the kobalt tool kit I bought my wife for Xmas last year has such a wrench, (could not get a socket on it) and the largest is the 36mm axle nut. (Could be wrong about that size, I’ll have to check when I get home, might be 32, don’t remember)

 

[MushCreek]

The axle nuts on my '72 F-250 are 2-9/16, or about 65 mm.

 

[BlackHorseSaga]

My BMW, and many others, use 46mm.

You can get dedicated hub nut sockets, which are a bit lighter / cheaper than some, but I have a 3/4 drive socket set, so no problem!

The same BMW uses 36mm for the oil filter. Again, you can get dedicated “oil filter” sockets, but if you have regular sockets in the appropriate sizes, you are always covered!

Generally speaking, if I need a tool once, I buy it - especially if it’s something multi purpose like a socket. I have never regretted this policy!

Germans use 46mm for weird things also. The internal oil filter housing bolt (which is hollow) on many Mercedes engines is a 46mm.

I have a whole set of Sunex sockets over 36mm in 1/2" drive for just that type of stupidity, but a 46mm Snap-on specifically for that bolt.

7mm is the smallest I've ever seen on a car. One bolt holding on the plastic wiring harness for an automtic transmission, and two 7mm nuts holding on the emblem on an Italian car.

 

[Michael_in_DE]

5.5mm holding up the bottom of a ford taurus front bumper. F'n stupid.

 

[nezzman]

7mm for jubilee clips, and used an 8mm for the bolts that hold on the EGR valve on my berlingo van.

I think the biggest I have needed is a 42mm for axle nuts on the back.

 

[Rc_Guy]

8mm to change air cleaner on my Jeep Gladiator

 

[Movin/on]

I think if you go back to the 1910's and 20's you would find some huge axle and spring nuts on the high end luxury cars.
I do have some spark plugs that have a 1-1/4 hex. not sure what they are from. I do have a Teen's Packard dust cover for an axle tht has 3" threads and provision for a 1-1/2 hex to remove/install it.
Movin/on

 

[ATC]

5.5mm on late-'80's Ford trucks holding parts of the grille and headlights/buckets on.
Lots of 7mm on the interior of Fords.

Lug nuts on my '88 F350 were 1-1/8"
Track bars on the front axle were pretty big...over 1.5" iirc
Pinion nuts
Pitman arm nuts

 

[silkman]

Definitely get sizes 30 and above in 12 point, because sometimes axle nuts are 12 point, and at that size, you're not going to round off any hex nuts even with a 12 point socket.

I would go and say 27mm and above if you don't have them, should be got in 12 point, deep and impact. Even if you don't have an impact gun you may get one in the future.

And as was said, buy the tools for the job beforehand. Even the most comprehensive socket set may not include what you need. The other day a mechanic friend was asking me where to get a 31mm socket, I think it was for a KTM or Ducati bike.

 

[BlackHorseSaga]

I would go and say 27mm and above if you don't have them, should be got in 12 point, deep and impact. Even if you don't have an impact gun you may get one in the future.

And as was said, buy the tools for the job beforehand. Even the most comprehensive socket set may not include what you need. The other day a mechanic friend was asking me where to get a 31mm socket, I think it was for a KTM or Ducati bike.

It was probably 1-3/16" or 1-1/4"

It really pays to have an entire set of sockets from 10-32mm (3/8 up to 19-21mm, and rest in 1/2").

Fasteners can be weird sizes sometimes. I use 1-3/4" sockets on 46mm sometimes if it's a better fit.

 

[NYBODYMAN]

Ford Crown Vic head light adjusters are 4.5 or 5.5mm IIRC. The only set the parts store had that went that small was a set of "ignition wrenches" which I imagine are for distributor components, but I've only had to work on more modern stuff.

Those old Ford headlamp adjusters were 4 and 4.5 mm. I have a few specialty wrenches just for that application. Ford also liked to use 5.5 mm's on bumpers, grills etc in the front end as well as in the interiors.

 

[Steve_P]

largest I've used is something like 35mm on axle nuts. Outside of that, anything over 19mm is uncommon, other than a balancer bolt

 

[Meursault74]

4 of 4.5 mm. I can't recall which. It was for the screws that held together the electrical to the mechanical portion of the anti-lock braking module. I swapped out the electrical portion as it was causing glitches all over the Camry.I think the screws were e-torx, but I'm not sure. I didn't have any of those e-torx , but one of those hex sockets I had fit and turned the screws out. Not a real high torque application.

 

[dchawk81]

You probably could, if the torque was low, but the dedicated oil filter sockets I’ve seen are very low profile, and wouldn’t engage properly on a nut or bolt head.

A proper 36mm socket, will of course do all tasks!

Not on some oil filter caps. You need the low profile to clear other things. That's why they exist.

 

[Ricky Joe]

I think if you go back to the 1910's and 20's you would find some huge axle and spring nuts on the high end luxury cars.
I do have some spark plugs that have a 1-1/4 hex. not sure what they are from. I do have a Teen's Packard dust cover for an axle tht has 3" threads and provision for a 1-1/2 hex to remove/install it.
Movin/on

I don’t remember ever working on anything that required more than 2-1/8” on antique cars. Old Dodge trucks required that for the axle nut. That might be the same size as Ford V8 oil drain plugs, I don’t remember, just reach for the wrench. Mercedes transmission electronic piece where the electrics go inside requires a 7mm, and the battery post was 9mm. I know there are smaller applications, but that’s what I remember.

 

[Milton Shaw]

The screws holding the module to the side of a Ford distributor were the smallest I have ever run into, biggest was axle nuts on floating rear bearings on super duty F250.

 

[lolaetype]

The way people drive today I'd say the biggest nut is often behind the wheel.

On my Jaguar the biggest nut is 1-5/16" and holds the harmonic balancer in place.

 

[isb cornbinder]

I found this large bolt inside the column of a camel-back drill press. The bolt is attached to a chain that threads up the inside of the drill press and attaches to the quill and acts as a counterbalance. The bolt body is 3 inches, and the hex-head is 5 inches.
I thought this was a good example of repurposing something for a new and different job.

 

[saltwater4life]

36mm axle nuts on my 1500 Sierra. Biggest I’ve had to use on anything. Popular size for many other applications also.

 

[humber2]

Rear axles using 6307 bearings (fitted to 35 mm shaft) use a 46 mm nut.

On English cars the Differential pinion, gearbox rear drive flange, engine front pulley, steering box drop arm and maybe the steering wheel are usually needing tools sized 3/4WW or 1 5/16” or 33mm.

For a longtime 1/2” drive SAE socket sets stopped at 1 1/4”, Whitworth sets topped out at 3/4

YMMV