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

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

In our third part of the thread determination UN thread, we would like to give you further insights from our everyday operations. We received a customer enquiry from a motor vehicle company that specialises in the repair of vintage cars. A bolt thread for the crankshaft housing should be determined. On the Internet you can often find the descriptions “Threaded bolt to the front crank pin” or “Axle, pin to the V-belt pulley, threaded bolt” or also “Threaded bolt for the crankshaft housing”.

In the following 3 steps we would like to describe how we have designed the threaded bolt for classic cars. The thread instructions should enable you to easily determine the thread yourself.

Let’s go!
Preparation for thread determination

To prepare for the thread determination of the vintage threaded bolt, we needed a thread template (metric and imperial), a caliper gauge and a technical thread table.

Step 1: Determine the threaded bolt diameter

To determine the diameter of the threaded bolt, please use a caliper gauge. Place the wide legs of the caliper gauge straight or at an angle on the threaded bolt.

Step 1: Determine outer diameter

With a digital calliper you will now see the diameter. With our threaded bolt for an oldtimer the diameter was 15.67 mm = 5/8″ inch

Step 2: Determine the pitch of the threaded bolt

To determine the pitch of the threaded bolt in the next step, you need a thread template. Try out all the blades until you find the one that fits.

This requires a very precise eye and care, as the pitch diameters 55 degrees and 60 degrees appear very similar. More about the differences can be found in the blog post:

The 13 most important thread types you should know

Step 2: Determining the gradient

On our bolt, the pitch was 16 gears per inch (inches to 25.4 mm) 1.587 mm pitch with a 60 degree flank angle.

Step 3: Look up the values in a technical table

In the last step, it is usually sufficient to look up the values in technical tables. Although the thread dimension is not a special thread, it is not very common in German-speaking countries.

Values to look up:

Threaded bolt diameter 15.67 mm = 5/8″
Pitch 16 gears per inch (inches to 25.4 mm)

Since the few will have these technical tables at home, we have provided a technical table with outside diameter, core hole diameter, thread name etc.

Technical table 12-UN thread (Unified Special Pitch)

Thread name	Outdoor- diameter (mm)	Core Hole- diameter (mm)	gears per inch	Steigung (mm)
7/16″ – 16-UN	11,112	9,576	16	1,587
1/2″ – 16-UN	12,700	11,200	16	1,587
9/16″ – 16-UN	14,288	12,800	16	1,587
5/8″ – 16-UN	15,875	14,400	16	1,587
11/16″ – 16-UN	17,462	16,000	16	1,587
13/16″ – 16-UN	20,637	19,100	16	1,587
7/8″ – 16-UN	22,225	20,700	16	1,587
15/16″ – 16-UN	23,813	22,300	16	1,587
1″ – 16-UN	25,400	23,900	16	1,587
1 1/16″ – 16-UN	26,987	25,500	16	1,587
1 1/8″ – 16-UN	28,575	27,100	16	1,587
1 3/16″ – 16-UN	30,162	28,700	16	1,587
1 1/4″ – 16-UN	31,750	30,300	16	1,587
1 5/16″ – 16-UN	33,337	31,750	16	1,587
1 3/8″ – 16-UN	34,925	33,400	16	1,587
1 7/16″ – 16-UN	36,512	35,000	16	1,587
1 1/2″ – 16-UN	38,100	36,600	16	1,587
1 9/16″ – 16-UN	39,688	38,200	16	1,587
1 5/8″ – 16-UN	41,275	39,800	16	1,587
1 11/16″ – 16-UN	42,862	41,350	16	1,587
1 3/4″ – 16-UN	44,450	43,000	16	1,587
1 13/16″ – 16-UN	46,037	44,500	16	1,587
1 7/8″ – 16-UN	47,625	46,100	16	1,587
1 15/16″ – 16-UN	49,212	47,700	16	1,587
2″ – 16-UN	50,800	49,300	16	1,587
2 1/8″ – 16-UN	53,975	52,600	16	1,587
2 1/4″ – 16-UN	57,150	55,650	16	1,587
2 3/8″ – 16-UN	60,325	58,850	16	1,587
2 1/2″ – 16-UN	63,500	62,000	16	1,587
2 5/8″ – 16-UN	66,675	65,150	16	1,587
2 3/4″ – 16-UN	69,850	68,350	16	1,587
2 7/8″ – 16-UN	73,025	71,500	16	1,587
3″ – 16-UN	76,200	74,700	16	1,587
3 1/8″ – 16-UN	79,375	77,850	16	1,587
3 1/4″ – 16-UN	82,550	81,000	16	1,587
3 3/8″ – 16-UN	85,725	84,200	16	1,587
3 1/2″ – 16-UN	88,900	87,400	16	1,587
3 5/8″ – 16-UN	92,075	90,550	16	1,587
3 3/4″ – 16-UN	95,250	93,750	16	1,587
3 7/8″ – 16-UN	98,425	96,900	16	1,587
4″ – 16-UN	101,600	100,100	16	1,587
4 1/8″ – 16-UN	104,775	103,300	16	1,587
4 1/4″ – 16-UN	107,950	106,450	16	1,587
4 3/8″ – 16-UN	111,125	109,600	16	1,587
4 1/2″ – 16-UN	114,300	112,800	16	1,587
4 5/8″ – 16-UN	117,475	116,000	16	1,587
4 3/4″ – 16-UN	120,650	119,150	16	1,587
4 7/8″ – 16-UN	123,825	122,300	16	1,587
5″ – 16-UN	127,000	125,500	16	1,587
5 1/4″ – 16-UN	133,350	131,850	16	1,587
5 1/2″ – 16-UN	139,700	138,200	16	1,587
5 5/8″ – 16-UN	142,875	141,350	16	1,587
5 7/8″ – 16-UN	149,225	147,750	16	1,587
6″ – 16-UN	152,400	150,900	16	1,587

It is a UN thread (Unified Special Pitch) with 16 turns per inch.

Tap DIN 2184-2/C 5/8-16 UN

Digression UN Unified with Special Pitch

The UN thread is an American thread with special pitch. A distinction is made between 8 threads per inch (8-UN), 12 threads (12-UN), 16 threads (16-UN) and 20 threads (20-UN). The flank angle for the UN thread is 60 degrees.