Free: Fraction to Decimal Table, in JPG and PDF

King Fan

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Sometimes an amp project requires measuring oddball amp bits with digital calipers to decide what size hole to drill. You can easily google huge drill size tables online, but I'm not interested in 90% of the 'drill sizes' they list, like size 53 or size J:

1653341504573.jpeg


So I made a simple table of fractions and decimals. If helpful, here's a pic, and I'll attach the PDF.

1653342152451.jpeg
 

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King Fan

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I should add: One reason I don't have to use calipers more often is the hole size info Doug Hoffman supplies on his website. Though I shared this somewhere in the past, FWIW here's my write-up of his notes and a few of my own:

From Doug Hoffman’s notes:
Screw and hole sizes:
#4 screws are .108 inches in diameter - Use a 7/64 inch drill bit
#6 screws are .132 inches in diameter - Use a 9/64 inch drill bit
#8 screws are .158 inches in diameter - Use a 11/64 inch drill bit
#10 screws are .186 inches in diameter - Use a 13/64 inch drill bit

Screw uses for common parts:
Use #4 screws to mount tube sockets
Use 4-40 x 1/4 inch long screws and #4 Keps nuts to mount the tube sockets
Some tube sockets have undersized mounting holes which need to be drilled out a bit larger for #4 screws; use a 7/64 inch drill bit for #4 screws
Use #4 screws for tube socket adapter plates
Use #6 screws for capacitor clamps
Use #6 screws for IEC receptacles
Use #6 or #8 screws for chokes
Use #6 screws for small output transformers
Use # 8 screws for large output transformers
Use #8 screws for power transformers
Use 8-32 x 5/8 inches long screws for your main ground screw by the power transformer
Use 8-32 x 5/8 inches long screws to mount the boards when using 1/4 tall standoffs
Use #10-24 screws / bolts to mount the chassis
Use oversized fender washers to clamp something to get a larger clamping area

My added notes:
The Fender lamp assembly fits an 11/16” hole
A 3/8” hole takes CTS pots, Switchcraft jacks, RCA jacks
Alpha pots come in at least two bushing diameters; some are 3/8” but many are the smaller .335”
A 1/2” hole takes:
• The shoulder washers used to isolate Switchcraft jacks
• Traditional Fender fuse holder — but check
• Many Carling switches
Carling mini-toggle switch fits in 1/4” hole — but check
Though made for a D-hole, Doug Hoffman’s standard Heyco strain relief will fit a 5/8” round hole
For ground anchors, I use Doug’s 8-32 X 3/8" screws with #8 ring terminals, star washer under ring, and Keps nut — plus a drop of thread locker
 

MickM

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Sometimes an amp project requires measuring oddball amp bits with digital calipers to decide what size hole to drill. You can easily google huge drill size tables online, but I'm not interested in 90% of the 'drill sizes' they list, like size 53 or size J:

View attachment 986347

So I made a simple table of fractions and decimals. If helpful, here's a pic, and I'll attach the PDF.

View attachment 986358
I was a Vo-Tech(machine shop) student in high school and had most fraction to decimal equivalents memorized by the time I graduated. A girlfriend's father worked as a machinist/tool maker for 30 years in the local steelmill and when she mentioned to him that I worked in a machine shop he gave me an impromptu fraction to decimal equivalents quiz. After I got the first 6 or 7 correct he figured I wasn't BS ing and we were buddies from then on. I haven't done that sort of work for over 30 years but still have those charts in my tool box.
 

King Fan

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I was a Vo-Tech(machine shop) student in high school and had most fraction to decimal equivalents memorized by the time I graduated. A girlfriend's father worked as a machinist/tool maker for 30 years in the local steelmill and when she mentioned to him that I worked in a machine shop he gave me an impromptu fraction to decimal equivalents quiz. After I got the first 6 or 7 correct he figured I wasn't BS ing and we were buddies from then on. I haven't done that sort of work for over 30 years but still have those charts in my tool box.
Fun story. I can sorta remember that 1/8 = 0.125, and on a really good day both logic and some numeric alignment remind me 3/8 = .375. But 11/64, not so much. :)
 

archetype

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Very useful, and thanks for that. My design and engineering background makes me think in decimals. I may be using a tape measure for woodworking, but I'm thinking in decimals.
 

SerpentRuss

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If you're like me, even if you save that on your phone, you're not likely to find it quickly, though you can always search for it on the web.

This is a simple method I use at work and at home where I have a complete set of drills by 64ths of an inch up to 1 inch in diameter. When I need to drill a hole for something I measure it with a caliper, multiply by 64 with a phone calculator, and then round up to the next highest number if it's not an exact integer. This tells me what drill to use. This method works with whatever division you have in your drill set, though some of your holes will get sloppier using 32nds or 16ths.

For example, say you measure 0.79 inches. 0.79 x 64 = 50.56, rounding up gets you to 51, so use a 51/64 drill. Only have drills by a 32nd? 0.79 x 32 = 25.28 round up to 26/32 which is of course 13/16.
 

Kevin Wolfe

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Thanks, that’s a nice piece of work sir.
I have a Starrett drill chart on my shop wall, which are free from them by the way, and use it often. I, however, do use number and letter drills in the gun work
It’d be cool if you’d arrange that and put it on a sticky.
A short list of wood screw hole sizes including the through hole and the thread pilot size is also very handy, especially for folks making cabs or guitars.
 




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