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<div>"BTW, Wondering what the "#8" of an 8-32 tap/die refers to. Wire Size?" </div>


<div>&nbsp;</div>


<div>Joe, it's a Universal Thread Standard (UTS) controlled by ANSI</div>


<div>&nbsp;</div>


<div>"The standard designation for a UTS thread is a number indicating the nominal (major) diameter of the thread, followed by the pitch measured in <A class=mw-redirect title="Threads per inch" href="http://en.wikipedia.org/wiki/Threads_per_inch">threads per inch</A>. For diameters smaller than ¼ inch, the diameter is indicated by an integer number defined in the standard, for all other diameters, the inch figure is given.</div>


<div>&nbsp;</div>

<TABLE class=wikitable width=800>
<CAPTION>Unified Screw Threads - UNC, UNF and UNEF <SUP id=cite_ref-1 class=reference jQuery17209929874252821067="16"><A href="http://en.wikipedia.org/wiki/Unified_Thread_Standard#cite_note-1"><FONT size=2><SPAN>[</SPAN>2<SPAN>]</SPAN></FONT></A></SUP></CAPTION>
<TBODY>
<TR>
<TH rowSpan=2>Major diameter<br>
[in (mm)]</TH>
<TH colSpan=3>Threads per inch (Pitch)</TH>
<TH colSpan=3>Tap drill size - Preferred sizes<SUP id=cite_ref-2 class=reference jQuery17209929874252821067="17"><A href="http://en.wikipedia.org/wiki/Unified_Thread_Standard#cite_note-2"><FONT size=2><SPAN>[</SPAN>3<SPAN>]</SPAN></FONT></A></SUP></TH></TR>
<TR>
<TH>Coarse (UNC)</TH>
<TH>Fine (UNF)</TH>
<TH>Extra fine (UNEF)</TH>
<TH>Coarse</TH>
<TH>Fine</TH>
<TH>Extra fine</TH></TR>
<TR>
<TD>#0 = 0.0600 (1.5240)</TD>
<TD>–</TD>
<TD>80</TD>
<TD></TD>
<TD></TD>
<TD>3/64 in</TD>
<TD></TD></TR>
<TR>
<TD>#1 = 0.0730 (1.8542)</TD>
<TD>64</TD>
<TD>72</TD>
<TD></TD>
<TD>#53</TD>
<TD>#53</TD>
<TD></TD></TR>
<TR>
<TD>#2 = 0.0860 (2.1844)</TD>
<TD>56</TD>
<TD>64</TD>
<TD></TD>
<TD>#50</TD>
<TD>#50</TD>
<TD></TD></TR>
<TR>
<TD>#3 = 0.0990 (2.5146)</TD>
<TD>48</TD>
<TD>56</TD>
<TD></TD>
<TD>#47</TD>
<TD>#45</TD>
<TD></TD></TR>
<TR>
<TD>#4 = 0.1120 (2.8448)</TD>
<TD>40</TD>
<TD>48</TD>
<TD></TD>
<TD>#43</TD>
<TD>#42</TD>
<TD></TD></TR>
<TR>
<TD>#5 = 0.1250 (3.1750)</TD>
<TD>40</TD>
<TD>44</TD>
<TD></TD>
<TD>#38</TD>
<TD>#37</TD>
<TD></TD></TR>
<TR>
<TD>#6 = 0.1380 (3.5052)</TD>
<TD>32</TD>
<TD>40</TD>
<TD></TD>
<TD>#36</TD>
<TD>#33</TD>
<TD></TD></TR>
<TR>
<TD>#8 = 0.1640 (4.1656)</TD>
<TD>32</TD>
<TD>36</TD>
<TD></TD>
<TD>#29</TD>
<TD>#29</TD>
<TD></TD></TR>
<TR>
<TD>#10 = 0.1900 (4.8260)</TD>
<TD>24</TD>
<TD>32</TD>
<TD></TD>
<TD>#25</TD>
<TD>#21</TD>
<TD></TD></TR>
<TR>
<TD>#12 = 0.2160 (5.4864)</TD>
<TD>24</TD>
<TD>28</TD>
<TD>32</TD>
<TD>#16</TD>
<TD>#14</TD>
<TD></TD></TR>
<TR>
<TD>1/4 = 0.2500 (6.3500)</TD>
<TD>20</TD>
<TD>28</TD>
<TD>32</TD>
<TD>#7</TD>
<TD>#3</TD>
<TD></TD></TR>
<TR>
<TD>5/16 = 0.3125 (7.9375)</TD>
<TD>18</TD>
<TD>24</TD>
<TD>32</TD>
<TD>F</TD>
<TD>I</TD>
<TD></TD></TR>
<TR>
<TD>3/8 = 0.3750 (9.5250)</TD>
<TD>16</TD>
<TD>24</TD>
<TD>32</TD>
<TD>5/16 in</TD>
<TD>Q</TD>
<TD></TD></TR>
<TR>
<TD>7/16 = 0.4375 (11.1125)</TD>
<TD>14</TD>
<TD>20</TD>
<TD>28</TD>
<TD>U</TD>
<TD>25/64 in</TD>
<TD></TD></TR>
<TR>
<TD>1/2 = 0.5000 (12.7000)</TD>
<TD>13</TD>
<TD>20</TD>
<TD>28</TD>
<TD>27/64 in</TD>
<TD>29/64 in</TD>
<TD></TD></TR>
<TR>
<TD>9/16 = 0.5625 (14.2875)</TD>
<TD>12</TD>
<TD>18</TD>
<TD>24</TD>
<TD>31/64 in</TD>
<TD>33/64 in</TD>
<TD></TD></TR>
<TR>
<TD>5/8 = 0.6250 (15.8750)</TD>
<TD>11</TD>
<TD>18</TD>
<TD>24</TD>
<TD>17/32 in</TD>
<TD>37/64 in</TD>
<TD></TD></TR>
<TR>
<TD>3/4 = 0.7500 (19.0500)</TD>
<TD>10</TD>
<TD>16</TD>
<TD>20</TD>
<TD>21/32 in</TD>
<TD>11/16 in</TD>
<TD></TD></TR>
<TR>
<TD>7/8 = 0.8750 (22.2250)</TD>
<TD>9</TD>
<TD>14</TD>
<TD>20</TD>
<TD>49/64 in</TD>
<TD>13/16 in</TD>
<TD></TD></TR>
<TR>
<TD>1 = 1.0000 (25.4000)</TD>
<TD>8</TD>
<TD>12</TD>
<TD>20</TD>
<TD>7/8 in</TD>
<TD>59/64 in</TD>
<TD></TD></TR></TBODY></TABLE>

<div>The following formula is used to calculate the major diameter of a numbered screw greater than or equal to 0: <I>Major diameter</I> = <I>Screw #</I> × 0.013" + 0.060". For example, a number 10 calculates as: #10 × 0.013" + 0.060" = 0.190" major diameter. "</div>


<div>&nbsp;</div>


<div>Your #8 screw calculates out to a major diameter of 0.164".&nbsp; I'm assuming they use size numbers&nbsp;for the same reason that other sizing standards have arisen - to avoid using a lot of decimal points.</div>


<div>&nbsp;</div>


<div>&lt;G&gt; Wikipedia is your friend!</div>


<div>&nbsp;</div>


<div><A href="http://en.wikipedia.org/wiki/Unified_Thread_Standard">http://en.wikipedia.org/wiki/Unified_Thread_Standard</A></div>


<div><A href="http://www.engineersedge.com/screw_threads_chart.htm">http://www.engineersedge.com/screw_threads_chart.htm</A></div>


<div>&nbsp;</div>


<div>C-</div>
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