STI Helicoil Drill Size Chart

NOMINAL	C/SINK DIA. - 120 DEG		SUGGESTED DRILL SIZE
THREAD SIZE	MINIMUM	MAXIMUN	ALUMINUM		STEEL, PLASTIC
			CUT TAP	FORM TAP	CUT TAP
UNIFIED COARSE
2 (0.086)-56	0.090	0.110	3/32 (0.0938)	#38 (0.1015)	#41 (0.096)
3 (0.099)-48	0.110	0.140		#43 (0.089)	7/64 (0.1094)
4 (0.112)-40	0.140	0.170	#31 (0.120)	3.3 MM (0.1299)	#31 (0.120)
5 (0.125)-40	0.160	0.190	3.4MM (0.1339)		#29 (0.136)
6 (0.138)-32	0.180	0.210	#26 (0.147)	4.1MM (0.1614)	#25 (0.1495)
8 (0.164)-32	0.200	0.230	#17 (0.173)	#12 (0.189)	#16 (0.177)
10 (0.190)-24	0.240	0.270	13/64 (0.2031)	5.7MM (0.2244)	#5 (0.2055)
12 (0.216)-24	0.260	0.290	#1 (0.228)		#1 (0.228)
1/4 (0.250)-20	0.310	0.340	H (0.266)	L (0.290)	H (0.266)
5/16 (0.3125)-18	0.380	0.410	Q (0.332)		Q (0.332)
3/8 (0.375)-16	0.450	0.480	X (0.397)		X (0.397)
7/16 (0.4375)-14	0.520	0.550	29/64 (0.4531)		29/64 (0.4531)
1/2 (0.500)-13	0.590	0.620	33/64 (0.5156)		17/32 (0.5312)
9/16 (0.5625)-12	0.660	0.690	37/64 (0.5781)		19/32 (0.5938)
5/8 (0.625)-11	0.730	0.760	21/32 (0.6562)		21/32 (0.6562)
3/4 (0.750)-10	0.870	0.900	25/32 (0.7812)		25/32 (0.7812)
7/8 (0.875)-9	1.000	1.030	29/32 (0.9062)		29/32 (0.9062)
1 (1.000)-7	1.140	1.170	1 1/32 (1.0312)		1 1/32 (1.0312)
1 1/8 (1.125)-7	1.290	1.320	1 11/64 (1.1719)		1 11/64 (1.1719)
1 1/4 (1.250)-7	1.410	1.440	1 19/64 (1.2969)		1 19/64 (1.2969)
1 3/8 (1.375)-6	1.560	1.590	1 27/64 (1.4219)		1 27/64 (1.4219)
1 1/2 (1.500)-6	1.690	1.720	1 35/64 (1.5469)		1 35/64 (1.5469)
UNIFIED FINE
3 (0.099)-56	0.110	0.140	#37 (0.104)		#36 (0.1065)
4 (0.112)-48	0.140	0.170	3 MM (0.1181)		#31 (0.120)
6 (0.138)-40	0.170	0.200	#26 (0.147)		#25 (0.1495)
8 (0.164)-36	0.200	0.230	#17 (0.173)		#16 (0.177)
10 (0.190)-32	0.230	0.260	#7 (0.201)	5.5MM (0.2165)	13/64 (0.2031)
1/4 (0.250)-28	0.290	0.320	G (0.261)		6.7MM (0.2638)
5/16 (0.3125)-24	0.360	0.390	21/64 (0.3281)		21/64 (0.3281)
3/8 (0.375)-24	0.420	0.450	25/64 (0.3906)		25/64 (0.3906)
7/16 (0.4375)-20	0.500	0.530	29/64 (0.4531)		29/64 (0.4531)
1/2 (0.500)-20	0.560	0.590	33/64 (0.5156)		33/64 (0.5156)
9/16 (0.5625)-18	0.630	0.660	37/64 (0.5781)		37/64 (0.5781)
5/8 (0.625)-18	0.690	0.720	41/64 (0.6406)		41/64 (0.6406)
3/4 (0.750)-16	0.820	0.850	49/64 (0.7656)		49/64 (0.7656)
7/8 (0.875)-14	0.960	0.990	57/64 (0.8906)		57/64 (0.8906)
1 (1.000)-14	1.080	1.110	1 1/64 (1.0156)		1 1/32 (1.0312)
1 (1.000)-12	1.100	1.130	1 1/64 (1.0156)		1 1/32 (1.0312)
1 1/8 (1.125)-12	1.220	1.250	1 9/64 (1.1406)		1 5/32 (1.1562)
1 1/4 (1.250)-12	1.350	1.380	1 17/64 (1.2656)		1 9/32 (1.2812)
1 3/8 (1.375)-12	1.470	1.500	1 25/64 (1.3906)		1 13/32 (1.4062)
1 1/2 (1.500)-12	1.600	1.630	1 33/64 (1.5156)		1 17/32 (1.5312)
METRIC
M2 X 0.4				#43 (0.0890)
M2.5 X 0.45				#34 (0.1110
M3 X 0.5			#43 (0.0890)	3.4MM (0.1339)	#44 (0.0860)
M3.5 X 0.6			#26 (0.1670)	#22 (0.1570)	#26 (0.1670)
M4 X 0.7			#19 (0.1660)	#15 (0.1800)	#19 (0.1660)
M5 X 0.8			#6 (0.2040)	#2 (0.2210)	#4 (0.2090)
M6 X 1.0			#D (0.2460)	#H (0.2660)	#E (0.2500)
M8 X 1.25			21/64 (0.3281)	9MM (0.3543)	#Q (0.3320 )