Tools, Sharpening and Power Machinery - SAE vs. Metric

Would greatly appreciate if someone can explain the difference between the two. I can use both on a nut so why buy one over the other? SAE has 5 sides right?

What is the rule of thumb to buy?

Thank You:thumbup:

Different measuring systems. SAE (Society of Automotive Engineers) is the old standard used in the US for fasteners, it is based on inches. Metric is based in meters, centimeters, millimeters etc and is the new US standard for automotive fasteners. The only vehicle I am aware of that still uses SAE fasteners is Harley Davidson. Some metric sizes overlap into SAE sizes which is why some of your sockets will fit both fasteners. For example a 1/2" wrench will roughly fit a 12mm bolt

I can;t say I have ever gotten a 1/2" wrench to fit anything metric well enough to use.

7/16 will fit 11mm
5/16 and 8 mm
9/16 and 14 mm

Basically, you use whatever fits the bolt/nut. If the fasteners are SAE, you buy SAE (inch) wrenched. If the fasteners are metric, you buy metric wrenches.

a typical common bolt/nut has 6 sides whether it be metric or SAE. You can generally buy 6 or 12 point box wrenches or sockets.

Check out the big box stores---many sets come with both sae & metric wrenches & socket sets.....................

Wish the US would just switch! Yes it will be a pain in the butt. But my oldest is in is 1st grade so maybe I can learn with her,

"For example a 1/2" wrench will roughly fit a 12mm bolt"

Unless I'm mistaken it's 13mm that is almost identical to 1/2"

Basically you will buy tools that fit what you work on. I have more SAE than metric but I've been buying tools since 1970 so I have more SAE than metric, plus I like older vehicles :D
My sons have more metric than SAE :p

A half inch would be 12.7mm if my math and memory are correct.

Different set of dogs! If you buy 6 point sockets when you buy standard, a lot of them will interchange with metric. The 12/16 point sockets won't(not in my experience-50 years cars and trucks 20 years on locomotives.) Buy the best you can afford and they will last a lifetime unless you are a professional.

12MM is about the only thing I can't find a cross over for. Some will be pretty sloppy but usually will work Bolt is realy stuck. 40 years in auto before I went to somethong else.

sae would be more correctly called fractional as they are measured in fractions of a inch.
metric is the world wide standard for the other nations of the industrial world. 13 mm close to 1/2 in. some 14mm will fit 9/16 some won't, 15mm sometimes will work for 9/16 but it depends on the fastning torque. always use the correct fiting wrench or socket and you will save yourself a lot of grief in the long run.
personaly other than womens measurments and speed i like metric sizing.

life begins when the kids leave home and the dog dies

I total agree that the metric system makes more sense..... but how do you teach an old dog new tricks?:eek::D