#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.

If you have any questions about thread determination, please do not hesitate to contact us. We will help you free of charge.

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