I am going to change my spark plugs today, and will be using the NGK Laser Iridium's for my 2008 Honda Fit Sport. I am so confused with lb/ft and ft/lb. I read a post on here that says to torque spark plugs to 13 lb/ft. Is that the same as ft/lb? is 13 ft/lb really the correct torque spec. I don't want to screw this up.

NGK's website shows: Aluminum Clyinder Head (lb-ft.), 14 mm, 18.0 - 21.6.

 

I say tom-ah-to, you say tom-ey-to! Same thing. I say foot pounds as most people do but I've it seen written as pounds per foot which has the same meaning. I don't have my service manual with me but 13 ft pounds sounds just about right for an aluminum head (it is a light torque value). Just for reference, the oil filter is only about 7 ft/lbs and the oil drain plug is about 30 ft/lbs so your value is right where it should be! Go ahead a torque away!

The one thing to watch out for are inch pounds (in.-lbs.). That's a different unit of torque. Most torque specs I've seen for my honda fit have always been in ft/lbs.

 

Agreed: lb-ft and ft-lb are the same thing. Dimensionally, it's just feet multiplied by pounds—that is to say, if you have a one foot long wrench, you need to push it with 13 pounds of force at the end to get the proper torque. If you have a six-inch wrench, it's 26 pounds of force that are required. The distance (of the lever arm) and the force are multiplied together to get the torque.

To be pedantic, I should note that this is quite different from lb/ft and from ft/lb, which imply division (pounds per foot or feet per pound) and which do not describe torque. I can't think of any measurements offhand that would have either of these units, but there are plenty where you do need to divide the units. For example, pressure may be measured in pounds per square foot, or lb/ft^2, though it's more commonly measured in pounds per square inch. (I have seen pounds per square foot used for things like floor and roof load ratings.)

 

Ok. Maybe shoulda used a hyphen instead of a slash. I didn't mean pound per foot. It's what DrewE said, a weight in pounds one foot away from the fulcrum.

 

Thanks again for your help!

 

Thanks for this information

 

None of the above. It's ft.lb using the standard mathematical term for multiply: '.'

Or, if you're evolving out of the Middle Ages into the 19th Century, N.m

 

Lb/Ft are when you turn the torque wrench to the right. Ft/Lb are when you turn it to the left.

 

If you want to be ultra-uber-precise, you should use a raised dot '·' rather than a period '.' for multiplication.

With metric units, the multiplication is often not shown explicitly, so Nm would also be correct. This should not be written as nm (which properly denotes nanometers), nor as mN (millinewtons).

All this is probably way more information than Letsclique bargained for.