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'.
"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,
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.
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 . . . . .
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
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
as they move over the tackwork.
Odd; I found some screws this size (3-48) at Micro Fasteners
(http://www.microfasteners.com ), but only in the form of alloy socket
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 ).
The only reason corrupt Republicans rule the roost in Washington
is because the corrupt Democrats can't muster any viable opposition.
I get mine from an industrial fastener supplier, but I also can get small
from any of several hardware stores within 10 or less miles of where I live.
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.
One last bit of number screw trivia:
The outside diameter of a number screw can be found by the following
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"?
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