View Full Version : A question for metric wrenchers. (15 mm & 18 mm)

05-25-2014, 02:49 PM
Those of you who use metric wrenches, do you ever come across a nut that requires a 15mm or an 18mm wrench?

P.I. Stazzer-Newt
05-25-2014, 02:56 PM
15 occasionally, 18 never.

Common sizes around that are 14, 17 and 19

05-25-2014, 03:03 PM
The serpentine belt tensioner on a '99 Ford Taurus takes a 15mm wrench. There are also some 15mm bolt heads in the front disc brake assemblies.



David G
05-25-2014, 03:04 PM
IIRC... we used my 18mm wrenches when helping a friend put together a HF trailer...

05-25-2014, 03:25 PM
I've used a 15 mm and a 19 mm on my motorcycles a few times (old Hondas), but don't recall ever using an 18 mm.

Paul Pless
05-25-2014, 03:27 PM
an 18mm wrench?what's that covert to in whitworth???

Monkey Butler
05-25-2014, 03:37 PM
15mm is quite common. I think Audi uses an 18mm on some suspension parts. Where you would use 19mm on the fastener and the 18mm on the other end to prevent rotation.

I have a set of sockets that has every metric size from 10mm to 32mm in 1mm increments. Ever use a 23mm socket?

Paul Pless
05-25-2014, 03:41 PM
must be a really slow day in vancouver. . .

P.I. Stazzer-Newt
05-25-2014, 03:48 PM
what's that covert to in whitworth???

How big of a hammer.

05-25-2014, 04:36 PM
Bellhousing bolts front wheel drive GMs


05-25-2014, 04:55 PM
Don't remember the exact relationship, Whitworth spanners are designated by thread diameter rather than size across the flats. In the marine trades ALL European machinery is metric. North American auto manufacturers have been using metric fasteners for at least thirty years. GM bellhousing bolts are 18 mm AF, and the bolt above the starter, on the back side is best removed with a ratcheting box end spanner, otherwise one needs to remove RH wheel assy and use about four feet of extension making for a very hairy job (don't ask me how I know:!)


05-25-2014, 04:58 PM
18mm recently for the first time but I can't remember where.

Jimmy W
05-25-2014, 05:21 PM
It seems like VW Bugs used a lot of 15s.

05-25-2014, 05:25 PM
Bicycle axle nuts and pedals are 15mm (outside the USA at least)

05-25-2014, 09:35 PM
It comes up once in a while, I several German diesels (Hatz, Deutz) and an 18 mm head is often found on connecting rod cap screws, head bolts, rocker shafts and other precision parts. It 's always sort of a surprise, but nothing else fits


Nicholas Carey
05-25-2014, 10:04 PM
The oddball metric sized sockets and wrenches are for working on the nearest English fastener after it's been bolluxed up by some goober with a pair of Vice-Grips.

Sent from my iPad using Tapatalk

05-25-2014, 11:19 PM
I needed an 18mm spanner recently when I replaced a Peugeot alternator belt. 15mm are quite common on Euro cars.

The Bigfella
05-25-2014, 11:26 PM
The Chinese will save you. Sorry, this one's imperial... but you get the idea


Hunky Dory
05-26-2014, 09:18 AM
15 fits Jeep Cherokee bumper bolts and lots of cars use 18 for suspension parts. From a body mans point of view. I find 14 and 9 the ones least used in my toolbox

05-26-2014, 02:54 PM
The oddball metric sized sockets and wrenches are for working on the nearest English fastener after it's been bolluxed up by some goober with a pair of Vice-Grips.

Sent from my iPad using Tapatalk.

My crew rounded off all my propane connections using vice grips, channel locks. Rather then reach for the right wench right in the tool box or ignore the wrench tied to the bottle..

Course they are roofers .

05-26-2014, 04:03 PM
14 and 15 mm nuts are common on e.g. bicycles. With the M8 thread, the standard nut is 13 mm. 16 mm and 18 mm used to be very uncommon so many tool sets omitted those. The standard nut for M10 thread has recently (within the last 1/4 of a century) changed to 16 mm, and for the M12 thread to 18 mm. The consequence is that many toolboxes miss those sizes now.

If 9 mm or 11 mm fits I check for the proper imperial tool instead.

And, yes, it's a cold and rainy day.


Nicholas Scheuer
05-26-2014, 06:12 PM
So what about 17mm? The nuts on the lower end of 10mm threaded rods securing my Albn-25's deck cleats are 17mm Bronze. That is a larger hex than a standard SS 10mm hex nut.

05-27-2014, 07:49 AM
7mm, 10mm, 13mm,15mm,17mm and 19mm as the most common. if you drop one overboard its a major loss. in between sizes are common on hydraulics and fitting that require two spanners to work

05-27-2014, 08:24 AM
I'm not sure just where, but I know I have used 18mm while working on some of our modern VW's, 15mm is commonly used on lots of things.

05-27-2014, 02:45 PM
This is a handy chart (pdf download) wrench and bolt head comparison chart, SAE, Metric, and Whitworth, in order of head size (http://www.triumphrat.net/attachments/classic-vintage-and-veteran/39402d1311714920-wrench-cross-reference-chart-bolt-head-comparison-chart.pdf)