Today I'll show you how to find the right wrench or socket to fit a bolt or nut
if you don't know if it's metric or standard, also how to identify markings on bolt heads,
which sizes are interchangeable, plus a little mechanic math.
There's a link in the description to download a handy chart
you can print on cardstock and keep in your toolbox.
This chart converts both standard and metric to thousandths of an inch
so they can be directly compared.
You may run into a mix of metric and standard bolts on the same vehicle,
especially on US cars and trucks from the 1970s and 80s.
Both foreign and newer US vehicles after 2000 are mostly metric,
but you might still find standard bolts on older components,
or parts like spark plugs, battery cables, lug nuts, or bleeder screws,
also tools and yard equipment.
You can see on this chart that 5/16 inch and 8 millimeter wrenches and sockets
are so close they are interchangeable.
5÷16 rounded up is 0.313 inches.
1 millimeter is .0394 inches,
multiply that by 8 mm equals 0.315 inches,
so we can see that 8 mm is only 2 thousandths inch bigger than 5/16",
which is extremely close.
This size is pretty common on hose clamps,
and the two wrenches or sockets fit basically the same.
If a wrench size is too small, like this 3/8 inch,
look at the chart for the next largest size, which is a 10 millimeter,
a very common size with no equivalent in SAE.
7/16" is way too big.
7/16" and 11 mm are only 4 thousandths of an inch different,
so they are interchangeable,
and either one fits this bolt on my rototiller just fine.
1/2 inch is often considered to be equal to 13 mm,
and either will work well in most cases,
but 1/2 inch is actually 12 thousandths of an inch smaller,
so if you have both available, and the half inch works, I would use it,
because you'll get a tighter fit, thus less chance of stripping.
Bolt head markings can get complex,
and often have a manufacturer's initials on them.
If you see radial lines its SAE,
also known as standard or Imperial.
If it has a number like 6 or 8.8 its metric.
This SAE construction bolt fits a half inch wrench.
It's a little loose in the 13 millimeter.
We know this bolt is metric because it says 8.8 on the head,
a common metric marking, and even though it's metric,
it fits nice and snug in the half inch wrench,
a little looser in the 13 millimeter.
You can tell by the 6 on this bolt that it's metric,
and a 14 millimeter fits it well.
9/16" fits it too, a little bit looser.
This standard SAE construction bolt also fits tighter in the 14 mm.
A 9/16" is too small for this nut on our engine mount,
the next size up is a 15 millimeter, very common size.
The 5/8" is way too loose - you'd strip the nut before you got it off -
so there's no substitute for a 15 mm.
And 5/8" is almost identical to a 16 mm.
A 17 mm will not go on this nut, but 11/16" fits just fine,
so we can see that they are Not interchangeable.
And lastly 3/4"is almost identical to 19 mm,
and there are man more that are interchangeable as the sizes get larger.
I found it very handy to have this chart,
which is in the description below the video.
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Thank you!