What are wire/number/letter drills used for?

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CarlosA

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Now, that is kind of a click bait title because we all know what most of them are used for.

More specifically: What are the odd drills in the range used for? For example a number 35 (.110") drill does not show up on any chart I have. But a number 30 shows up for a metric tap m4 .7, or a number 33 shows up for a 6-40 tap thread. A number 33 shows up for the body size of a 4-36,40,48 machine screw. I would say maybe the #35 is for a reamer, but the closest reamer is 7/65" at .109" - Drilling for an oversized reamer for a 7/64 would still be too sloppy. A number 36 drill is .111" - is there ever a reason to ream a #36 hole?

So what are the rest of the drills used for? I have not really researched this yet, just curious what you all think.
 
CarlosA said:
Now, that is kind of a click bait title because we all know what most of them are used for.

More specifically: What are the odd drills in the range used for? For example a number 35 (.110") drill does not show up on any chart I have. But a number 30 shows up for a metric tap m4 .7, or a number 33 shows up for a 6-40 tap thread. A number 33 shows up for the body size of a 4-36,40,48 machine screw. I would say maybe the #35 is for a reamer, but the closest reamer is 7/65" at .109" - Drilling for an oversized reamer for a 7/64 would still be too sloppy. A number 36 drill is .111" - is there ever a reason to ream a #36 hole?

So what are the rest of the drills used for? I have not really researched this yet, just curious what you all think.
Click to expand...
They are used for whatever you need them for, whether it is an orifice to control air, oil, or water, for making starter holes for wood and sheet metal screws in various materials, if you want a bit looser hole for tapping in hard materials, etc. They help you to make the size hole you think you need for a job. If drill bits came in .001" (or .01mm) increments like gage pins, I would be tempted to buy a set...
 
I have several sets of 61-80 for doing appliance and automotive jetting. Never really pursued the why of it. He who is there first makes the rules, pertains to many things. Mike
 
kd4gij said:
Drilling holes that size.:dunno:
Click to expand...
Entirely to obvious.
Number drills are for drilling holes in numbers.
Letter drills are for drilling holes in letters except for the letter Q, the letter Q can not be drilled at all, it's a nasty little bugger.
Likewise fractional drills will drill fractions in 1/64" increments, if you require 1/128" increments this requires a non sinusoidal high modulus zero size drill.

Hope this helps
 
I have used a D drill (0.246) to put bearing races (1/4-1/8-3/32 ball bearings:: 0.250) in Al so that the bearings can be pushed in with thumb pressure but not fall out under vibration nor gravity. I simply use calipers or micrometers and measure the thing being fitted, then run some tests in spare material to check for fits.

Once you get smaller than about 1/3rd of an inch (8mm) you depend more on drilling and less on boring.
 
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