Drill Size Table

(This page revised October 25, 2023)

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Every pen restorer who does extensive work will sooner or later run up against the need to drill holes.

The charts on this page list number gauge drill sizes from 1 to 80 and letter gauge drill sizes from A to Z, along with fractional sizes that fall into the range, and indicates tap and clearance sizes for Imperial and metric screws. There are also a few notes on sizes that are particularly useful for certain specific pen-related tasks such as clearing stuck sac remnants from Touchdown and Snorkel sac guards.

Number Gauge Drill Sizes (Go to Letter Gauge Sizes)
Number	Fraction	Decimal	Use		Number	Fraction	Decimal	Use
80		0.0135			40		0.0980
79		0.0145			39		0.0995	3-48 clearance hole
		0.0156
78		0.0160	Clear 0.5 mm pencil lead		38		0.1015	5-40 tap drill
77		0.0180			37		0.1040	2.5 mm clearance hole Parker BP refill clearance
76		0.0200			36		0.1065	6-32 tap drill
							0.1094
75		0.0210			35		0.1100
74		0.0225			34		0.1110
73		0.0240	Clear 0.7 mm pencil lead		33		0.1130	4-40 clearance hole
72		0.0250			32		0.1160
71		0.0260			31		0.1200
							0.1250	3.0 mm clearance hole
70		0.0280			30		0.1285	4.0 mm tap drill
69		0.0292	Waterman lever pivot pin holes		29		0.1360	5-40 clearance hole 8-32 tap drill
68		0.0310			28		0.1405	6-32 clearance hole
		0.0312					0.1406
67		0.0320	Clear 0.9 mm pencil lead		27		0.1440
66		0.0330			26		0.1470
65		0.0350			25		0.1495
64		0.0360			24		0.1520
63		0.0370			23		0.1540
							0.1562
62		0.0380			22		0.1570
61		0.0390	00-90 tap drill, Clear 1.1 mm pencil lead		21		0.1590
60		0.0400			20		0.1610	4.0 mm clearance hole
59		0.0410			19		0.1660	8-32 clearance hole
58		0.0420			18		0.1695
							0.1719
57		0.0430	Clear many vintage cap breather holes; drill out “51” sterling breather tube from feed		17		0.1720
56		0.0465	Push out Snorkel tube center feed		16		0.1770
		0.0469
55		0.0520	00-90 clearance hole 0-80 tap drill 1.6 mm tap drill		15		0.1800
54		0.0550			14		0.1820
53		0.0595	1-72 tap drill		13		0.1850
		0.0625					0.1875
52		0.0635	0-80 clearance hole 1.6 mm clearance hole 2.0 mm tap drill		12		0.1890
51		0.0670			11		0.1910
50		0.0700	2-56 tap drill		10		0.1935
49		0.0730			9		0.1960
48		0.0760	1-72 clearance hole		8		0.1990
		0.0781
47		0.0785	3-48 tap drill		7		0.2010
							0.2031
46		0.0810	2.0 mm clearance hole 2.5 mm tap drill		6		0.2040
45		0.0820			5		0.2055
44		0.0860			4		0.2090
43		0.0890	2-56 clearance hole 4-40 tap drill 2.0 mm clearance hole 3.0 mm tap drill		3		0.2130
							0.2187
42		0.0935			2		0.2210	Clear Snorkel sac guards
		0.0937
41		0.0960			1		0.2280
Letter Gauge Drill Sizes (Go to Number Gauge Sizes)
Letter	Fraction	Decimal	Use		Letter	Fraction	Decimal	Use
A		0.2340	Clear Touchdown TM & Imperial sac guards		N		0.3020
		0.2344					0.3125
B		0.2380			O		0.3160
C		0.2420			P		0.3230
							0.3282
D		0.2460			Q		0.3320
E		0.2500			R		0.3390
							0.3438
F		0.2570			S		0.3480
G		0.2610			T		0.3580
		0.2656					0.3594
H		0.2660	Clear PFM & ’49 Touch- down sac guards		U		0.3680
							0.3750
I		0.2720			V		0.3770
J		0.2770			W		0.3860
							0.3906
K		0.2810			X		0.3970
		0.2813
L		0.2900			Y		0.4040
							0.4063
M		0.2950			Z		0.4130
		0.2969

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