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Drill Bit Size Chart to 1/4 inch Diameter

Legend:   Number Drill   Fractional Inch   Letter Drill   Millimeters 
 Millimeters   Inches   Designation   Tap Drill/Pilot Drill Uses 
.3429mm .0135" #80  
.3683mm .0145" #79  
.3969mm .015625" 1/64" #0 Pilot
.4064mm .016" #78  
.4572mm .018" #77  
.5mm .0197"    
.508mm .02" #76  
.5334mm .021" #75  
.5715mm .0225" #74  
.6096mm .024" #73  
.635mm .025" #72  
.6604mm .026" #71  
.7112mm .028" #70  
.74168mm .0292" #69  
.75mm .0295"   M1x.25 coarse
.7874mm .031" #68  
.7938mm .03125" 1/32" #0 Pilot
.8128mm .032" #67  
.8382mm .033" #66  
.85mm .0335"   M1.1x.25 coarse
.889mm .035" #65  
.9144mm .036" #64  
.9398mm .037" #63  
.95mm .0374"   M1.2x.25 coarse
.9652mm .038" #62  
.9906mm .039" #61  
1mm .0394"    
1.016mm .04" #60  
1.0414mm .041" #59  
1.0668mm .042" #58  
1.0922mm .043" #57  
1.1mm .0433"   M1.4x.3 coarse
1.1811mm .0465" #56  
1.1906mm .046875" 3/64" #0-80 UNF
1.25mm .0492"   M1.6x.35 coarse
1.3mm .0512"   M1.7x.35 coarse
1.3208mm .052" #55  
1.397mm .055" #54  
1.45mm .0571"   M1.8x.35 coarse
1.5mm .0591"    
1.5113mm .0595" #53 #1-64 UNC, #1-72 UNF
1.5875mm .0625" 1/16"
1.6mm .063"   M2x.4 coarse
1.6129mm .0635" #52  
1.7018mm .067" #51  
1.75mm .0689"   M2.2x.45 coarse
1.778mm .07" #50 #2-64 UNF, #2-56 UNC
1.8542mm .073" #49  
1.9304mm .076" #48  
1.9844mm .078125" 5/64"
1.9939mm .0785" #47 #3-48 UNC
2mm .0787"    
2.05mm .0807"   M2.5x.45 coarse
2.0574mm .081" #46  
2.0828mm .082" #45 #3-56 UNF
2.1844mm .086" #44  
2.2606mm .089" #43 #4-40 UNC
2.3749mm .0935" #42 #4-48 UNF
2.3813mm .09375" 3/32"
2.4384mm .096" #41  
2.4892mm .098" #40  
2.5mm .0984"   M3x.5 coarse
2.5273mm .0995" #39  
2.5781mm .1015" #38 #5-40 UNC
2.6416mm .104" #37 #5-44 UNF
 
 Millimeters   Inches   Designation   Tap Drill/Pilot Drill Uses 
2.7051mm .1065" #36 #6-32 UNC
2.7781mm .109375" 7/64"
2.794mm .11" #35  
2.8194mm .111" #34  
2.8702mm .113" #33 #6-40 UNF
2.9mm .1142"   M3.5x.6 coarse
2.9464mm .116" #32  
3mm .1181"    
3.048mm .12" #31  
3.175mm .125" 1/8"
3.2639mm .1285" #30  
3.3mm .1299"   M4x.7 coarse
3.4544mm .136" #29 #8-32 UNC, #8-36 UNF
3.5mm .1378"   M4x.5 Fine
3.5687mm .1405" #28 #6 Screw
3.5719mm .140625" 9/64"
3.6mm .1417"   M4x.35 Fine
3.6576mm .144" #27  
3.7mm .1457"   M4.5x.75 coarse
3.7338mm .147" #26  
3.7973mm .1495" #25 #10-24 UNC
3.8608mm .152" #24  
3.9116mm .154" #23  
3.9688mm .15625" 5/32"
3.9878mm .157" #22  
4mm .1575"    
4.0386mm .159" #21 #10-32 UNF
4.0894mm .161" #20  
4.2mm .1654"   M5x.8 coarse
4.2164mm .166" #19 #8 Screw
4.3053mm .1695" #18  
4.3656mm .171875" 11/64"
4.3942mm .173" #17 #12-24 UNC
4.4958mm .177" #16  
4.5mm .1772"   M5x.5 Fine
4.572mm .18" #15 #12-28 UNF
4.6228mm .182" #14  
4.699mm .185" #13  
4.7625mm .1875" 3/16"
4.8006mm .189" #12 AN3 Bolt
4.8514mm .191" #11  
4.9149mm .1935" #10
4.9784mm .196" # 9  
5mm .1969"   M6x1 coarse
5.0546mm .199" # 8  
5.1054mm .201" # 7 1/4"-20 UNC
5.1594mm .203125" 13/64"
5.1816mm .204" # 6  
5.2197mm .2055" # 5  
5.25mm .2067"   M6x.75 Fine
5.3086mm .209" # 4  
5.4102mm .213" # 3 1/4"-28 UNF
5.5mm .2165"   M6x.5 Fine
5.5563mm .21875" 7/32"
5.6134mm .221" # 2  
5.7912mm .228" # 1  
5.9436mm .234" A  
5.9531mm .234375" 15/64"  
6mm .2362"   M7x1 coarse
6.0452mm .238" B  
6.1468mm .242" C  
6.2484mm .246" D 1/16"-27 NPT
6.25mm .2461"   M7x.75 Fine
6.35mm .25" 1/4", E AN4 Bolt
7.9375mm .3125" 5/16" 3/8"-16 UNC, AN5 Bolt
View this chart for up to 1" drill sizes 


When using a drill bit for a feeler gauge, please remember that many drill bits are actually undersize at the shank end of the drill bit so please use the above bit sizes with a grain of salt!

Also note that to correct for a broad feeler gauge or a loose-fitting drill bit:

ROC = (D2-W2)/8T
Where:
  • W = the width of the feeler gauge, or if the drill bit can be moved back and forth under the straight edge by the total amount W
  • D = mirror diameter,
  • T = gauge thickness or bit diameter.
Data borrowed from: Bob May's astronomy page.
 
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