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# Stupid cad jockeys forgot fractions

#### Bill D

##### Diamond
I need to figure out the hole spacing for an electrical outlet. All the drawings I can find online are in decimal inches or metric. I know it is in fractions since it was designed in the USA over 100 years ago but I can not figure it out.
On previous work it is some weird denominators I seldom use like 17/64
2.38"
3.28

#### memphisjed

##### Stainless
2 3/8 is 2.375 which is 2.38 for anyone but a machinist.

3.28 is 3 9/32.

#### john.k

##### Diamond
Show anyone under 30 a list of fractions and its .."All these crazy numbers are doing my head in"

#### Bill D

##### Diamond
2 3/8 is 2.375 which is 2.38 for anyone but a machinist.

3.28 is 3 9/32.
I figured out the 2.38 is 2 +11/32
EDIT: I meant 12/32 which is 3/8, so 2+3/8
Now to measure the round hole needed for the single outlet port. Not nearly as critical since it can be a bit oversize. kind of has to be oversize to allow for casting fillet at the base.
BilLD

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#### gregormarwick

##### Diamond
I figured out the 2.38 is 2 +11/32
Now to measure the round hole needed for the single outlet port. Not nearly as critical since it can be a bit oversize. kind of has to be oversize to allow for casting fillet at the base.
BilLD
2-3/8 is much closer to 2.38 than 2-11/32...

#### guythatbrews

##### Stainless
Show anyone under 30 a list of fractions and its .."All these crazy numbers are doing my head in"
I suspect every generation has said something similar of those coming up behind. Is American Machinist magazine still around. I liked the 100 years ago story on the back page. It really drove this point home.

Anyway with computers you don't need to know fractions! I had a high school civics teacher brag to the class he told his kids he didn't care if they flunked all their math classes, since they could just use a pocket calculator. Circa 1975. Most dipshit, useless teacher I ever had.

Bill D, at the very least get a decimal equivalents chart.

#### EPAIII

##### Diamond
I have a Greenlee chassis punch for the double D outline of the holes in a US standard duplex outlet (115V, 15/20 Amps). You are probably right about the original dimensions of these outlets being in fractions of an inch, but that was most likely for the outlets themselves and not for the cutouts in the covers, which had to be just a bit bigger. And perhaps things changed a bit over the years.

This is my working drawing which I use whenever I use that punch to create a mount for the duplex outlets, which I have done a number of times. The dimensions on it are from a combination of my best guess at the original, fractional dimensions, measurements of the chassis punch and the holes it makes, and from measurements taken from a number of different brands and quality levels of outlets. They DO WORK. If you round to fractional values, particularly if you round down, better have a file handy to make the outlet fit.

Anyway, for what it is worth, here is my working drawing. All dimensions are in decimal inches. Some are for fractional values and others are not.

And perhaps, just perhaps, with most of the outlets being made overseas, the manufacturers are rounding those original fractions to more even numbers in mm. So 3 1/4" becomes 82.5mm which then is 3.248". And there goes your fraction.

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#### GregSY

##### Diamond
It drives me nuts when someone uses .38 to represent 3/8"...or .12 to represent 1/8"....three decimal places is THE standard for anything expressed on raw numbers. If it's not that fussy, then use the fraction. 2-3/8" not 2.38" People have been murdered over less....

#### Philabuster

##### Diamond
It drives me nuts when someone uses .38 to represent 3/8"...or .12 to represent 1/8"....three decimal places is THE standard for anything expressed on raw numbers. If it's not that fussy, then use the fraction. 2-3/8" not 2.38" People have been murdered over less....
Some drafting software does not have fractions so decimals is all you get. The part that pisses me off is when a dimension that is obviously a fraction like 7/16" gets printed out as .4375" and is now a 4 place decimal tolerance per the print. That is when I want to murder someone.

#### guythatbrews

##### Stainless
It drives me nuts when someone uses .38 to represent 3/8"...or .12 to represent 1/8"....three decimal places is THE standard for anything expressed on raw numbers. If it's not that fussy, then use the fraction. 2-3/8" not 2.38" People have been murdered over less....
I don't like it either but not sure there is a standard, although I agree in conversation one should never say 2.38 if 2-3/8 is meant. OP got his number from a drawing, where two place decimals are very common.

I have a customer that calls out material this way, .63 is 5/8 stock. It confuses the bejesus out of their purchasing department. They supply material for their jobs, which is great by the way. I've requested .625 round and they reply they have none in stock, will .63 work?. Trying to play their game I've requested .63 round to receive the reply their supplier says .63 is a special mill run and very expensive and will 5/8 work? I can't win. Just a few weeks ago I received 5/16 round instead of the requested 9/16 round. Their purchasing ordered .56 round and the vendor heard 5/16.

Fractions can bite you in the ass too. A long-time machinist from another company designed an assembly and we were to make it. The guy was very, very proud he had used fractions in the design so it would be "easier to program". I'm thinking ok, 1/4 and 1/2 that's fine. He meant 32nds and 64ths. What a pain.

I was sure my kids learned fractions, not that they appreciated my tutelage at the time. My wife told me later she never understood fractions very well and learned along with the kids.

#### Scottl

##### Diamond
2 3/8 is 2.375 which is 2.38 for anyone but a machinist.

3.28 is 3 9/32.
Absolutely. The best way for the OP to handle this is to make a cheat sheet in something like Excel with the division results set to 2 digits displaying.

Another is to get one of those cheapo digital calipers that can display in decimal inches, metric, or fractional inches and use it as a units converter.

#### guythatbrews

##### Stainless
Oh, come on. We barely got this fraction stuff figured out and we gotta switch to metric? 2-3/8 mm is even more confusing!

#### Bill D

##### Diamond
2-3/8 is much closer to 2.38 than 2-11/32...
Opps, I meant 12/32 which is 3/8. My brain was tired last night. I will change it in the previous post.
Bill D

Wait for it...

#### Bill D

##### Diamond
My stupid digital caliper does convert to fractions. But it often uses weird denominators never seen on a ruler.
Like 0.73 is 11/15.
The online fraction converters just tell me that 0.38 is 38/100.
Bill D.

#### MilGunsmith

##### Stainless
You also have the problem of some of CAD software rounds off numbers. The Pro-E (Creo) that they use here rounds off to 2 decimal places if you dont change the parameters in the settings. For example, enter .375" and it rounds to .38", .4375" becomes .44". This might be where some of these numbers your seeing are coming from.

#### michiganbuck

##### Diamond
The other lost art is figuring out a percentage.
Next, the art of counting things will be lost.
A good thing that door knobs go both ways or people would get locked in their houses..

#### John Garner

##### Titanium
Machine screw and tapped hole thread specifications are my pet peeve. I firmly contend that the drawing citations should be consistent with the tap and die markings and fastener packages.

I formed this belief in the early 1980s, after having to explain why it's ok to install a #8-32 screw into a 0.164-0.03125 tapped hole.

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