[pianotech] screw sizes and TPI

[Joseph Garrett]

Chris, (I think), said:
""BTW, Wondering what the "#8" of an 8-32 tap/die refers to. Wire Size?" 
 
Joe, it's a Universal Thread Standard (UTS) controlled by ANSI
 
"The standard designation for a UTS thread is a number indicating the
nominal (major) diameter of the thread, followed by the pitch measured in
threads per inch. For diameters smaller than ? inch, the diameter is
indicated by an integer number defined in the standard, for all other
diameters, the inch figure is given.
 
 
Unified Screw Threads - UNC, UNF and UNEF [2]
 
Major diameter
[in (mm)]
Threads per inch (Pitch)
Tap drill size - Preferred sizes[3]
 
Coarse (UNC)
Fine (UNF)
Extra fine (UNEF)
Coarse
Fine
Extra fine
 
#0 = 0.0600 (1.5240)
?
80
 
 
3/64 in
 
 
#1 = 0.0730 (1.8542)
64
72
 
#53
#53
 
 
#2 = 0.0860 (2.1844)
56
64
 
#50
#50
 
 
#3 = 0.0990 (2.5146)
48
56
 
#47
#45
 
 
#4 = 0.1120 (2.8448)
40
48
 
#43
#42
 
 
#5 = 0.1250 (3.1750)
40
44
 
#38
#37
 
 
#6 = 0.1380 (3.5052)
32
40
 
#36
#33
 
 
#8 = 0.1640 (4.1656)
32
36
 
#29
#29
 
 
#10 = 0.1900 (4.8260)
24
32
 
#25
#21
 
 
#12 = 0.2160 (5.4864)
24
28
32
#16
#14
 
 
1/4 = 0.2500 (6.3500)
20
28
32
#7
#3
 
 
5/16 = 0.3125 (7.9375)
18
24
32
F
I
 
 
3/8 = 0.3750 (9.5250)
16
24
32
5/16 in
Q
 
 
7/16 = 0.4375 (11.1125)
14
20
28
U
25/64 in
 
 
1/2 = 0.5000 (12.7000)
13
20
28
27/64 in
29/64 in
 
 
9/16 = 0.5625 (14.2875)
12
18
24
31/64 in
33/64 in
 
 
5/8 = 0.6250 (15.8750)
11
18
24
17/32 in
37/64 in
 
 
3/4 = 0.7500 (19.0500)
10
16
20
21/32 in
11/16 in
 
 
7/8 = 0.8750 (22.2250)
9
14
20
49/64 in
13/16 in
 
 
1 = 1.0000 (25.4000)
8
12
20
7/8 in
59/64 in
 
 
 
The following formula is used to calculate the major diameter of a numbered
screw greater than or equal to 0: Major diameter = Screw # ? 0.013" +
0.060". For example, a number 10 calculates as: #10 ? 0.013" + 0.060" =
0.190" major diameter. "
 
Your #8 screw calculates out to a major diameter of 0.164". I'm assuming
they use size numbers for the same reason that other sizing standards have
arisen - to avoid using a lot of decimal points.
 
<G> Wikipedia is your friend!
 
http://en.wikipedia.org/wiki/Unified_Thread_Standard
http://www.engineersedge.com/screw_threads_chart.htm
 
C-hris,
That's the most confusing thing ever concieved, imo! Who the heck is
"ANSI"? (hate all this alphabet soup we are constantly deluged with, just
because people are too lazy to say/write what they really mean! imho!<G>
hehe I copied all of that to show that the "times" signs were changed to
question marks, so wondering what else didn't translate with these darned
'puters!???? the formulae is based on What? And who was the whiz kid that
thunked that up? Most confusing to say the least. (metric isn't any better
in my olde eyes either!
So, IF I wanted to make a bolt, which I do often, there should be some
corresponding sizes in steel and brass rod, shouldn't there? As far as I
know there isn't. Give me more info please? Also, that "chart" is post WWII
and is not relevant to a lot of the stuff we have to deal with in the "pre
WWII" pianos. Best example is Chickerings. They seemed to get great joy out
of using really odd sizes of bolts and screws. (If they were alive today,
I'd personally throttle the whole lot!<G> Example per yours there is/was a
1/4-30 before WWII.<G> I actually have one of those tap/die sets.(came from
our local Go To Hardware people.) AND, while we're at it, what the heck is
a 1/4-#7???!!! That's a real lulu~!
That's my take on that.
Joe
Joe Garrett, R.P.T.
Captain of the Tool Police
Squares R I