Drill question

Does anyone know the correct drill size to drill a hole to be threaded with a number 56 tap?
Thanks, Jeff

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#51
http://www.engineersedge.com/tap_drill_chart.htm
Cheers,
Colin
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Jeff Stanton wrote:

presumably you mean a 2-56 tap. That's a number 2 machine screw with 56 threads per inch.
The correct drill to be used when tapping any particular size hole is called the 'tap drill' for that size. For a larger hole that the screw slides through freely, it's called the 'clearance drill'.
The tap drill for a 2-56 size is either #50 or #51. The correct tap drill size depends on how 'full' a thread one desires (how deep the thread is cut compared to a perfect "V" shape) ... it's almost NEVER 100%. The industry-standard thread is 75%, which determines the appropriate tap drill as given on drill charts. For a 2-56 either the #50 or #51 will be close to that desired size.
Be aware that, for ANY size screw, there are two common (and many more uncommon) thread pitches. Each combination of screw size and thread pitch requires a DIFFERENT tap drill.
Thus your original question of a number 56 screw is meaningless in and of itself, as it could refer to any of several screw sizes (3-56 for instance). However, since 2-56 is one of the most common screw sizes used in modeling, one can deduce that that's what you meant.
The *COMMON* screw sizes of interst to model railroaders are: 00-90; 0-80, 1-72, 2-56, 3-48, and 4-40.
In that same size range there are many, MANY others less common, many are 'English', and yet others 'Metric'.
Dan Mitchell ===========
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3-48 common???
I haven't come across anyplace to purchase 3-48 screws or taps in years.
Norm
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Norm Dresner wrote:

"OK", perhaps not COMMON, but it's the standard size between #2 and #4, and as such can be VERY useful, occasionally. I agree it's far less common than either the 2-56 or 4-40 sizes, but it's still around. They're encountered fairly often in electronics and instruments among other things. Some older model trains used them. You'll also find them in model aircraft and RC cars occasionally. Like all fasteners, many are now being replaced with metric equivalanets.
Most regular fastener or machine tool sources should have such 3-48 screws, taps, or dies (example: MSC, Wholesale tool, Traverse, Fastener-Express, etc.).
If you mean that your local hobby shop, Walthers, or Micro-Mart doesn't have them, I'm not surprised. If they did, they likely wouldn't be worth much anyway, as is generally true of most drills, taps, or dies purchased in hobby stores.
So, if you're just repairing newer items, you probably won't encounter the 3-48 size. But, if your're repairing older things, or scratchbuilding, it's a quite useful size to be able to deal with.
3-48 is certainly very, VERY 'common' compared with some of the screw sizes I have to sometimes deal with (1/8",3/16" #7, #9, unusual thread pitches or thread profiles, Whitworths, etc.). Not to mention all the scads of metric 'bastards' about ... anyone who thinks the metric fastener system is 'standardized' has never tried to work with it.
Dan Mitchell ===========
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wrote:

You can say that again.

You can say that again.
Try using the same tools on a Mercedes that you use on a Honda. - - - - N O T ! - - - - Same head - - different pitch Same pitch - - different head and so on and on it goes . . . . .
Froggy,
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Well there is English metric (Honda, I think) and then there is European metric and the list goes on.
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Jon Miller wrote:

So much for standardization. I'll stick with SAE.
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Screw sizes 3-48 and 5-40 are still used. The 5-40 size is extensively used in electronics applications. Almost all screw-type barier strips use 5-40 screws
I use 3-48 to attach HO scale trucks, because they allow me to put a collar over the screw and spring-load the truck. Spring-loaded trucks always track better than trucks held on by the screw head. They will not woble, but will still swing and flex as they move over the tackwork.
Froggy,
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Where do you purchase them? Norm
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Norm Dresner spake thus:

Odd; I found some screws this size (3-48) at Micro Fasteners (http://www.microfasteners.com ), but only in the form of alloy socket screws:
http://www.microfasteners.com/catalog/products/SSCSCA.cfm
For some reason, they don't seem to have any other "regular" screws (like flat-head, Philips, filister head, etc.) in this size. Likewise with Small Parts (http://www.smallparts.com ).
--
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I get mine from an industrial fastener supplier, but I also can get small quantities from any of several hardware stores within 10 or less miles of where I live. There are three within a five-mile radius of me.
Forget Home Despot or Lowes or any of the other mainstream "homer" stores of that type. They don't have a clue.
Froggy,
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Daniel A. Mitchell wrote:

One last bit of number screw trivia:
The outside diameter of a number screw can be found by the following formula:
D = .060" + (# x .013")
where D is the outside diameter and # is the number of the screw.
So a #5 screw is:
D5 = .060" + (5 x .013") = .125"
I'm not sure if a #00 fits the pattern. Maybe you subtract .013"?
Bill MacIndoe

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