Thread determination

How do I determine a thread?

We get customer inquiries again and again with the request to determine the thread. For this reason, we have decided to publish the thread specifications and to write down our procedure step-by-step as instructions. Gradually, more instructions for thread determination will appear in this section.

The aim of this series of articles is to enable you to determine your own thread at the end of the day!

In order to determine an unknown thread, two specifications are necessary: the pitch and the outer diameter for the bolt thread and the inner diameter for the nut thread.

The pitch of a thread is the distance from one flank to the other in mm for the metric system or the number of turns per inch for the inch thread

First measure the diameter of the thread with a calliper. Using the conversion table below, you can determine the inch dimension as a metric dimension and convert it. By definition, one inch is 25.4 mm. The diameter therefore tells you whether the thread is metric or inch.

Then the thread template is used. Please check the individual thread templates until one of the templates can be fitted exactly into the threads. Then read off the desired pitch, which is printed on the thread template.

Now use the enclosed caliper gauge, which contains all the information on the individual thread types. If no information is available to give a sufficiently reliable result, we recommend that you first repeat the series of measurements, as there may be a measuring error. If you are not successful here, please contact us directly. We will be glad to help you.

Step-by-step instructions for thread determination:

#1 Practical example: 3 steps for thread determination (1/4 inch)

#2 Practical example: 3 steps for thread determination (M12 Metric)

#3 Practical example: 3 steps for thread determination (Oldtimer 16-UN Unified Special Pitch)

Conversion table: Thread comparison table

Ø	Inch Decimal	BSW	UNC	UNF	UNEF	BSF	core-Ø	cone-Ø	threading-Ø


		thread pro 1″	thread pro 1″	thread pro 1″	thread pro 1″	thread pro 1″
Nr. 0	0,0598			80			1,2	1,49	1,52
Nr. 1	0,0728		64	72			1,5	1,79	1,85
Nr. 2	0,0858		56	64			1,8	2,1	2,18
Nr. 3	0,0992		48	56			2,1	2,41	2,52
Nr. 4	0,1122		40	48			2,4	2,77	2,85
Nr. 5	0,1248		40	44			2,6	3,09	3,17
Nr. 6	0,1378		32	40			2,9	3,41	3,5
Nr. 8	0,1638		32	36			3,5	4,02	4,16
Nr. 10	0,1902		24	32			4	4,71	4,83
Nr. 12	0,2161		24	28	32		4,6	5,37	5,49
1/16″	0,0625	60					1,2	1,55	1,587
3/32″	0,0937	48					1,9	2,3	2,381
1/8″	0,125	40					2,6	3,09	3,175
5/32″	0,1563	32					3,2	3,88	3,969
3/16″	0,1875	24				32	3,8	4,61	4,762
7/32″	0,2187	24				28	4,6	5,43	5,556
1/4″	0,25	20	20	28	32	26	5,1	6,17	6,35
5/16″	0,3125	18	18	24	32	22	6,5	7,76	7,938
3/8″	0,375	16	16	24	32	20	7,9	9,3	9,525
7/16″	0,4375	14	14	20	28	18	9,3	10,9	11,113
1/2″	0,5	12	13	20	28	16	10,5	12,44	12,7
9/16″	0,5625		12	18	24	16	12,3	13,9	14,288
5/8″	0,625	11	11	18	24	14	13,5	14,82	15,876
11/16″	0,6875				24	14	16,5	17,05	17,463
3/4″	0,75	10	10	16	20	12	16,5	18,76	19,051
13/16″	0,8125				20	12	19,5	20,33	20,638
7/8″	0,875	9	9	14	20	11	19,5	21,9	22,226
15/16″	0,9375				20	11	22,5	23,49	23,813
1″	1	8	8	12	20	10	22	25,08	25,4
1 1/16″	1,0625				18		25,5	26,63	26,988
1 1/8″	1,125	7	7	12	18	9	25	28,11	28,576
1 3/16″	1,1875				18		28,7	29,75	30,163
1 1/4″	1,25	7	7	12	18	9	28	31,35	31,751
1 5/16″	1,3125				18		32	32,9	33,338
1 3/8″	1,375	6	6	12	18	8	30,5	34,49	34,926
1 7/16″	1,4375				18		35	36,2	36,512
1 1/2″	1,5	6	6	12	18	8	33,5	37,67	38,101
1 5/8″	1,625	5	5		18	8	35,5	41	41,277
1 3/4″	1,75	5	5		18	7	39	44	44,452
1 7/8″	1,875	4,5	4,5		18		41,5	47,22	47,627
2 „	2	4,5	4,5		18	7	44,5	50,3	50,8
2 1/4″	2,25	4	4,5				50,8	56,75	57,152
2 1/2″	2,5	4	4				57,15	63,05	63,502
2 3/4″	2,75	3,5	4				62	69,25	69,853
3″	3	3,5	4				68,95	75,75	76,203

Core hole diameters are standard values,
which may vary depending on the number of gears.

Click here to download the thread comparison table free of charge

Here you can find thread determination sets