1inch = 25.4mm

5/16 = 25.4x5/16 = 7.937mm

Cách đọc ốc 4-40x1/2

Bảng tra cứu ốc UNC:

Đường kính ren (in)	Số ren trên inch	Đường kính ren (in)	Đường kính ren (mm)	Tap Drill Size (mm)	Pitch (mm)
#1 - 64	64	0.073	1.854	1.50	0.397
#2 - 56	56	0.086	2.184	1.80	0.453
#3 - 48	48	0.099	2.515	2.10	0.529
#4 - 40	40	0.112	2.845	2.35	0.635
#5 - 40	40	0.125	3.175	2.65	0.635
#6 - 32	32	0.138	3.505	2.85	0.794
#8 - 32	32	0.164	4.166	3.50	0.794
#10 - 24	24	0.190	4.826	4.00	1.058
#12 - 24	24	0.216	5.486	4.65	1.058
1/4" - 20	20	0.250	6.350	5.35	1.270
5/16" - 18	18	0.313	7.938	6.80	1.411
3/8" - 16	16	0.375	9.525	8.25	1.587
7/16" - 14	14	0.438	11.112	9.65	1.814
1/2" - 13	13	0.500	12.700	11.15	1.954
9/16" - 12	12	0.563	14.288	12.60	2.117
5/8" - 11	11	0.625	15.875	14.05	2.309
3/4" - 10	10	0.750	19.050	17.00	2.540
7/8" - 9	9	0.875	22.225	20.00	2.822
1" - 8	8	1.000	25.400	22.85	3.175
1 1/8" - 7	7	1.125	28.575	25.65	3.628
1 1/4" - 7	7	1.250	31.750	28.85	3.628
1 3/8" - 6	6	1.375	43.925	31.55	4.233
1 1/2" - 6	6	1.500	38.100	34.70	4.233
1 3/4" - 5	5	1.750	44.450	40.40	5.080
2" - 4 1/2	4 1/2	2.000	50.800	46.30	5.644
2 1/4" - 4 1/2	4 1/2	2.250	57.150	52.65	5.644
2 1/2" - 4	4	2.500	63.500	58.50	6.350
2 3/4" - 4	4	2.750	69.850	64.75	6.350
3" - 4	4	3.000	76.200	71.10	6.350
3 1/4" - 4	4	3.250	82.550	77.45	6.350
3 1/2" - 4	4	3.500	88.900	83.80	6.350
3 3/4" - 4	4	3.750	95.250	90.15	6.350
4" - 4	4	4.000	101.600	96.50	6.350

Example - Typical designation of an UNC thread

Tra cứu ốc UNF

Major Diameter (in)	Threads per inch	Major Diameter (in)	Major Diameter (mm)	Tap Drill Size (mm)	Pitch (mm)
#0 - 80	80	0.060	1.524	1.25	0.317
#1 - 72	72	0.073	1.854	1.55	0.353
#2 - 64	64	0.086	2.184	1.90	0.397
#3 - 56	56	0.099	2.515	2.15	0.453
#4 - 48	48	0.112	2.845	2.40	0.529
#5 - 44	44	0.125	3.175	2.70	0.577
#6 - 40	40	0.138	3.505	2.95	0.635
#8 - 36	36	0.164	4.166	3.50	0.705
#10 - 32	32	0.190	4.826	4.10	0.794
#12 - 28	28	0.216	5.486	4.70	0.907
1/4" - 28	28	0.250	6.350	5.50	0.907
5/16" - 24	24	0.313	7.938	6.90	1.058
3/8" - 24	24	0.375	9.525	8.50	1.058
7/16" - 20	20	0.438	11.112	9.90	1.270
1/2" - 20	20	0.500	12.700	11.50	1.270
9/16" - 18	18	0.563	14.288	12.90	1.411
5/8" - 18	18	0.625	15.875	14.50	1.411
3/4" - 16	16	0.750	19.050	17.50	1.587
7/8" - 14	14	0.875	22.225	20.40	1.814
1" - 12	12	1.000	25.400	23.25	2.117
1 1/8" - 12	12	1.125	28.575	26.50	2.117
1 1/4" - 12	12	1.250	31.750	29.50	2.117
1 3/8" - 12	12	1.375	43.925	32.75	2.117
1 1/2" - 12	12	1.500	38.100	36.00	2.117

Example - Typical designation of an UNF thread