Technical Problems In Measuring Nut Sizes
Technical Problems in Measuring Nut Sizes
- Nut sizes by the standard are referred to by their across flat measurement or AF. This is easy on an uninstalled nut. However, this gets a little dodgy when measuring across the flats of an installed nut. When a nut is installed, most procedures will require at least 3 threads are extending above the top face of the nut. These extending threads tend to block access from the measurement on the top. The stud also extends further than the corners of the nut flats and get in the way. Such that technician needs to “eyeball” or visually guess the proper measurement bend the ruler or use some form of trickery to get a measurement. Vernier calipers can reach across the flats without the stud getting in the way. However, they are too accurate as they measure in .0001” of an inch.
- The standard set by ASME has a minimum and maximum size envelope of acceptance. That is to say that the maximum of a 2” AF nut would measure exactly 2” (2.000”) but it has a minimum (Yet acceptable and called a 2” nut) size of about 1-15/16” (1.938”). This under-sizing of the nut can be frustrating if it is measured with a pair of Vernier calipers. Vernier calipers are very precise as they measure in thousands of an inch and are commonly used by machinists and inspection personnel. If they are expecting a 2” nut, it will seem to be off from the industry standard as they measure under-size of what is expected.
- Heavy Hex Metric and Imperial (fraction) size as set by ASME, ANSI, and ISO Common sizes are not what most would expect to find. Particularly if it is an installed nut with the stud in the way.
It is not uncommon that:
- 1-7/16” gets misinterpreted as 1-1/2” (as it is only 1/16” under)
- 1-13/16” gets misinterpreted as 1-3/4” (as it is only 1/16” over)
- 2-15/16” gets misinterpreted as 3” (as it is only 1/16 under)
- 4-5/8” gets misinterpreted as 4-1/2” (as it is only 1/8” over)
- To the end of accurately finding the correct nut size, the technician may use a tape or ruler which has increments of 1-1/8”, 1/16”, 1/32” or 1/64” thinking the more ticks, the more accurate it will be. However, this attempt at rigorous precision only serves to confuse the technician. He has about 20 standard Imperial Heavy Hex sizes and/or 25 standard Heavy Hex metric sizes but has to sift through all those tick marks to make a selection. Having a rule that only shows the Industry Standard Sizes makes for easier size identification.
- It is expensive when an incorrect nut size has been determined. On a bridge, reactor or wind turbine, it’s a long climb up. The wrench or hydraulic wrench set-up may weigh 130 lbs. Also, when the part of a job-scope where the nut is removed, if it isn’t removed, the job stops. Along with the other workers, support, safety, maintenance, engineering, crane operators, spotters, and assistants. All that preparation that went into getting ready for this job, Rent a Crane & operator, build scaffolding, volumes of permitting and planning, management of change. The Work Permits which are time stamped and have to be reissued at the end of each shift. Then there is the timeline, which is now extended; so the loss of uptime which can be an opportunity cost in the millions per day of lost production, for some plants. Particularly, if you’re the Technician with the wrench, who will turn the nut. The egg lands first on your face. It is very important to get the measurement right the first time.
FAQ - Frequently Asked Questions
Can I personalize it and put my name & contact info on it?
Yes. I need to know the spelling and your preferred font. Also, I could make a few examples for you to choose from. I do impressively beautiful full-color photos with the plastic and powder-coat versions.
The tick line is not exactly at the corner of the nut. Is something off?
No. This is normal. The nuts are undersized. Example: A 2" nut can be 1-15/16" across flats and still be called a 2" nut. It needs to be smaller to make it easy to install and remove a socket or wrench. 2" is the nominal size and 1-15/16" is the actual size.
Is the tick line on the Heavy Hex Gauge the actual size indicated?
Yes. The tick line on the Heavy Hex Gauge® is the actual size. Remember, the nuts are undersized. Think of the tick line as a, "Not to exceed" line. Since the nut is sure to be smaller than 2", think of it as a range. If the corner exceeds the 2" line, You should be looking for a 2-3/16" socket or wrench.
Why not show every 16th like a ruler?
You want to find the ASME B18.2.2 Standard size because that is what you will find on the tool crib shelf. or your tool rental company's bin. Sure they could make a 1-15/16" hydraulic torque link but that is expensive and it would be a very tight fit. You need a 2" tool in this example.
Can I put a picture on it?
Yes. The best process for beautiful full-color photos is the metal powder-coat version. You can buy these in any quantity. Just send me the photo and I'll mock it up for you.