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Drill Bit Size Chart to 1 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
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"  
 
Millimeters Inches Designation Tap Drill/Pilot Drill Uses
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" AN4 Bolt
6.35mm .25" E  
6.5mm .2559"    
6.5278mm .257" F 5/16"-18 UNC
6.6294mm .261" G  
6.7469mm .265625" 17/64"
6.7564mm .266" H  
6.8mm .2677"   M8x1.25 coarse
6.9088mm .272" I 5/16"-24 UNF
7mm .2756"   M8x.5 Fine
7.0358mm .277" J  
7.1374mm .281" K  
7.1438mm .28125" 9/32"  
7.25mm .2854"   M8x.75 Fine
7.366mm .29" L  
7.493mm .295" M  
7.5mm .2953"   M8x1 Fine
7.5406mm .296875" 19/64"
7.6708mm .302" N  
7.8mm .3071"   M9x1.25 coarse
7.9375mm .3125" 5/16" 3/8"-16 UNC, AN5 Bolt
8mm .315"   M9x1 Fine
8.0264mm .316" O  
8.2042mm .323" P  
8.3344mm .328125" 21/64"
8.4328mm .332" Q 3/8"-24 UNF
8.5mm .3346"   M10x1.5 coarse
8.6106mm .339" R 1/8"-27 NPT
8.7313mm .34375" 11/32"  
8.8mm .3465"   M10x1.25 Fine
8.8392mm .348" S  
9mm .3543"   M10x1 Fine
9.0932mm .358" T 7/16"-14 UNC
9.1281mm .359375" 23/64"  
9.25mm .3642"   M10x.75 Fine
9.3472mm .368" U  
9.5mm .374"   M11x1.5 coarse
9.525mm .375" 3/8"  
9.5758mm .377" V  
9.8044mm .386" W  
9.9219mm .390625" 25/64" 7/16"-20 UNF
10mm .3937"   M11x1 Fine
10.0838mm .397" X  
10.2mm .4016"   M12x1.75 coarse
10.2616mm .404" Y  
10.3188mm .40625" 13/32"  
10.4902mm .413" Z  
10.5mm .4134"   M12x1.5 Fine
10.7156mm .421875" 27/64" 1/2"-13 UNC
11mm .4331"   M12x1 Fine
11.1125mm .4375" 7/16" 1/4"-18 NPT
11.25mm .4429"   M12x.75 Fine
11.5mm .4528"    
11.5094mm .453125" 29/64" 1/2"-20 UNF
11.9063mm .46875" 15/32"  
12mm .4724"   M14x2 coarse
12.3031mm .484375" 31/64" 9/16"-12 UNC
12.5mm .4921"   M14x1.5 Fine
12.7mm .5" 1/2"  
12.8mm .5039"   M14x1.25 Fine
13mm .5118"   M14x1 Fine
13.0969mm .515625" 33/64" 9/16"-18 UNF
13.4938mm .53125" 17/32" 5/8"-11 UNC
13.5mm .5315"    
13.8906mm .546875" 35/64"  
14mm .5512"   M16x2 coarse
14.2875mm .5625" 9/16" 5/8"-18 UNF
14.5mm .5709"   M16x1.5 Fine
14.6844mm .578125" 37/64" 3/8"-18 NPT
15mm .5906"   M16x1 Fine
15.0813mm .59375" 19/32"  
15.4781mm .609375" 39/64"  
15.5mm .6102"   M18x2.5 coarse
15.875mm .625" 5/8"  
16mm .6299"   M18x2 Fine
16.2719mm .640625" 41/64" 3/4"-10 UNC
16.5mm .6496"    
16.6688mm .65625" 21/32"  
17mm .6693"   M18x1 Fine
17.0656mm .671875" 43/64"  
17.4625mm .6875" 11/16" 3/4"-16 UNF
17.5mm .689"   M20x2.5 coarse
17.8594mm .703125" 45/64" 1/2"-14 NPT
18mm .7087"   M20x2 Fine
18.2563mm .71875" 23/32"  
18.5mm .7283"   M20x1.5 Fine
18.6531mm .734375" 47/64"  
19mm .748"   M20x1 Fine
19.05mm .75" 3/4"  
19.4469mm .765625" 49/64" 7/8"-9 UNC
19.5mm .7677"   M22x2.5 coarse
19.8438mm .78125" 25/32"  
20mm .7874"   M22x2 Fine
20.2406mm .796875" 51/64"  
20.5mm .8071"   M22x1.5 Fine
20.6375mm .8125" 13/16" 7/8"-14 UNF
21mm .8268"   M24x3 coarse M22x1 Fine
21.0344mm .828125" 53/64"  
21.4313mm .84375" 27/32"  
21.5mm .8465"    
21.8281mm .859375" 55/64"  
22mm .8661"   M24x2 Fine
22.225mm .875" 7/8" 1"-8 UNC
22.5mm .8858"   M24x1.5 Fine
22.6219mm .890625" 57/64"  
23mm .9055"    
23.0188mm .90625" 29/32" 1"-12 UNF
23.4156mm .921875" 59/64" 3/4"-14 NPT
23.5mm .9252"    
23.8125mm .9375" 15/16"  
24mm .9449"   M27x3 coarse
24.2094mm .953125" 61/64"  
24.5mm .9646"   M26x1.5 Fine
24.6063mm .96875" 31/32"  
25mm .9843"   M27x2 Fine
25.0031mm .984375" 63/64" 1-1/8"-7 UNC
25.4mm 1.000" 1"  
View a smaller chart for up to 1/4" 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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