[Shop-talk] Metric wrenches

[Darrell Walker]

Hi David,

On May 27, 2011, at 8:37 PM, David Scheidt wrote:

> Standards, so many to choose from.   There are three common metric
> bolt standards.[1] For a given diameter, JIS will be smaller (above
> 6mm.  6mm and below, they're mostly the same.  except for really small
> stuff, which are a different set of standards.)  JIS use 12mm heads
> for 8mm bolts and 14 for 10mm, which are pretty common car stuff.  DIN
> use 13 and 17 mm heads for those sizes (except where they don't,
> because they've decided that 17 is just too big and will shear bolts.)
> ISO use 13 and 16.  Bigger than that, I'd have to look it up.
>
> Who knows what Triumph was doing on the TR8.  (sounds like DIN, which
> I don't hink has any even sizes above 6mm (10mm head) until they get
> really big (30mm heads on 20ish mm bolts)



Thanks for the explanation.

Most of the metric bolts on the TR8 seem to be 10 and 12 mm (17 and 19 mm
heads).  There are a few 8 mm (13 mm head), and it seems like I've used the 15
mm somewhere, maybe on the oversized nuts that hold the brake line ends.
There are some 6mm bolts (holding the front brake dust shield), those might
have been a 10 mm head).

You really have to pay attention because some of the metric sizes fit pretty
well in imperial wrenches.  Generally the engine is imperial (I suppose
because of it's Buick history), and most of the rest is metric.  But there are
some exceptions that don't seem to make any sense.  For example, the rear
suspension links are 7/16" bolts, while the front uses 12mm.   Except for the
ball joints, which are 1/2"....

So much for the superiority of the metric system!  (I know, it isn't the
system's fault, it is the competing standards).