Thread Die & Die Stock Size Chart.
Cutting a clean external thread by hand relies on three things: a rod turned to the correct diameter, the right die for your thread and a die stock to grip and turn that die. The part most people get wrong is matching the die stock to the die, because a die stock is sized by the outside diameter (OD) of the die it holds, not by the thread itself.
This page brings the numbers together in one place. Use the rod size chart to turn your metric bar to the correct diameter, the die size tables to match your thread to the right die and the die stock size chart to match that die to the stock that holds it. The die sizes cover metric coarse, metric fine and imperial threads, including UNC, UNF, BSW, BSF and BA.
Contents:
Rod Size for Thread Dies
When a die cuts an external thread it removes metal to form the thread flanks, so the diameter you turn your rod (blank) to becomes the major diameter of the finished thread. Turn the rod to the recommended diameter below, then chamfer the leading end so the die starts square. A blank that is even slightly oversize makes the die hard to start and can tear the thread crests, so it is better to sit a touch under than over.
The recommended figures are the maximum major diameter for a standard 6g external thread, calculated from the ISO 965 metric thread standard. For general work, aim within about 0.05 mm below the diameter shown. Imperial figures follow the equivalent basis, the Class 2A maximum major diameter for Unified threads and the nominal major diameter for Whitworth and BA.
Metric Coarse Rod Sizes
|
Thread |
Pitch (mm) |
Nominal Ø (mm) |
Recommended rod Ø (mm) |
|---|---|---|---|
|
M1.6 |
0.35 |
1.60 |
1.58 |
|
M2 |
0.40 |
2.00 |
1.98 |
|
M2.5 |
0.45 |
2.50 |
2.48 |
|
M3 |
0.50 |
3.00 |
2.98 |
|
M3.5 |
0.60 |
3.50 |
3.48 |
|
M4 |
0.70 |
4.00 |
3.98 |
|
M5 |
0.80 |
5.00 |
4.98 |
|
M6 |
1.00 |
6.00 |
5.97 |
|
M7 |
1.00 |
7.00 |
6.97 |
|
M8 |
1.25 |
8.00 |
7.97 |
|
M10 |
1.50 |
10.00 |
9.97 |
|
M12 |
1.75 |
12.00 |
11.97 |
|
M14 |
2.00 |
14.00 |
13.96 |
|
M16 |
2.00 |
16.00 |
15.96 |
|
M18 |
2.50 |
18.00 |
17.96 |
|
M20 |
2.50 |
20.00 |
19.96 |
|
M22 |
2.50 |
22.00 |
21.96 |
|
M24 |
3.00 |
24.00 |
23.95 |
Metric Fine Rod Sizes
|
Thread |
Pitch (mm) |
Nominal Ø (mm) |
Recommended rod Ø (mm) |
|---|---|---|---|
|
M6 x 0.75 |
0.75 |
6.00 |
5.98 |
|
M8 x 1.0 |
1.00 |
8.00 |
7.97 |
|
M10 x 1.0 |
1.00 |
10.00 |
9.97 |
|
M10 x 1.25 |
1.25 |
10.00 |
9.97 |
|
M12 x 1.25 |
1.25 |
12.00 |
11.97 |
|
M12 x 1.5 |
1.50 |
12.00 |
11.97 |
|
M14 x 1.5 |
1.50 |
14.00 |
13.97 |
|
M16 x 1.5 |
1.50 |
16.00 |
15.97 |
|
M18 x 1.5 |
1.50 |
18.00 |
17.97 |
|
M20 x 1.5 |
1.50 |
20.00 |
19.97 |
Unified Coarse (UNC) Rod Sizes
|
Thread |
Threads per inch |
Nominal major Ø |
Recommended rod Ø |
|---|---|---|---|
|
No. 4 (4-40) |
40 |
0.1120 in (2.84 mm) |
0.1112 in (2.82 mm) |
|
No. 6 (6-32) |
32 |
0.1380 in (3.51 mm) |
0.1372 in (3.48 mm) |
|
No. 8 (8-32) |
32 |
0.1640 in (4.17 mm) |
0.1631 in (4.14 mm) |
|
No. 10 (10-24) |
24 |
0.1900 in (4.83 mm) |
0.1890 in (4.80 mm) |
|
1/4 in |
20 |
0.2500 in (6.35 mm) |
0.2489 in (6.32 mm) |
|
5/16 in |
18 |
0.3125 in (7.94 mm) |
0.3113 in (7.91 mm) |
|
3/8 in |
16 |
0.3750 in (9.53 mm) |
0.3737 in (9.49 mm) |
|
7/16 in |
14 |
0.4375 in (11.11 mm) |
0.4361 in (11.08 mm) |
|
1/2 in |
13 |
0.5000 in (12.70 mm) |
0.4985 in (12.66 mm) |
|
9/16 in |
12 |
0.5625 in (14.29 mm) |
0.5609 in (14.25 mm) |
|
5/8 in |
11 |
0.6250 in (15.88 mm) |
0.6233 in (15.83 mm) |
|
3/4 in |
10 |
0.7500 in (19.05 mm) |
0.7482 in (19.00 mm) |
|
7/8 in |
9 |
0.8750 in (22.23 mm) |
0.8731 in (22.18 mm) |
|
1 in |
8 |
1.0000 in (25.40 mm) |
0.9980 in (25.35 mm) |
Unified Fine (UNF) Rod Sizes
|
Thread |
Threads per inch |
Nominal major Ø |
Recommended rod Ø |
|---|---|---|---|
|
No. 4 (4-48) |
48 |
0.1120 in (2.84 mm) |
0.1113 in (2.83 mm) |
|
No. 6 (6-40) |
40 |
0.1380 in (3.51 mm) |
0.1372 in (3.48 mm) |
|
No. 8 (8-36) |
36 |
0.1640 in (4.17 mm) |
0.1632 in (4.15 mm) |
|
No. 10 (10-32) |
32 |
0.1900 in (4.83 mm) |
0.1891 in (4.80 mm) |
|
1/4 in |
28 |
0.2500 in (6.35 mm) |
0.2490 in (6.32 mm) |
|
5/16 in |
24 |
0.3125 in (7.94 mm) |
0.3114 in (7.91 mm) |
|
3/8 in |
24 |
0.3750 in (9.53 mm) |
0.3739 in (9.50 mm) |
|
7/16 in |
20 |
0.4375 in (11.11 mm) |
0.4362 in (11.08 mm) |
|
1/2 in |
20 |
0.5000 in (12.70 mm) |
0.4987 in (12.67 mm) |
|
9/16 in |
18 |
0.5625 in (14.29 mm) |
0.5611 in (14.25 mm) |
|
5/8 in |
18 |
0.6250 in (15.88 mm) |
0.6236 in (15.84 mm) |
|
3/4 in |
16 |
0.7500 in (19.05 mm) |
0.7485 in (19.01 mm) |
|
7/8 in |
14 |
0.8750 in (22.23 mm) |
0.8734 in (22.18 mm) |
|
1 in |
12 |
1.0000 in (25.40 mm) |
0.9982 in (25.35 mm) |
Whitworth Coarse (BSW) Rod Sizes
For Whitworth threads the maximum major diameter equals the nominal size, so the figure below is both the nominal major diameter and the diameter to turn the rod to. Sit a touch under.
|
Thread |
Threads per inch |
Major Ø (turn rod to just under) |
|---|---|---|
|
1/8 in |
40 |
0.1250 in (3.18 mm) |
|
3/16 in |
24 |
0.1875 in (4.76 mm) |
|
1/4 in |
20 |
0.2500 in (6.35 mm) |
|
5/16 in |
18 |
0.3125 in (7.94 mm) |
|
3/8 in |
16 |
0.3750 in (9.53 mm) |
|
7/16 in |
14 |
0.4375 in (11.11 mm) |
|
1/2 in |
12 |
0.5000 in (12.70 mm) |
|
9/16 in |
12 |
0.5625 in (14.29 mm) |
|
5/8 in |
11 |
0.6250 in (15.88 mm) |
|
3/4 in |
10 |
0.7500 in (19.05 mm) |
|
7/8 in |
9 |
0.8750 in (22.23 mm) |
|
1 in |
8 |
1.0000 in (25.40 mm) |
Whitworth Fine (BSF) Rod Sizes
|
Thread |
Threads per inch |
Major Ø (turn rod to just under) |
|---|---|---|
|
3/16 in |
32 |
0.1875 in (4.76 mm) |
|
1/4 in |
26 |
0.2500 in (6.35 mm) |
|
5/16 in |
22 |
0.3125 in (7.94 mm) |
|
3/8 in |
20 |
0.3750 in (9.53 mm) |
|
7/16 in |
18 |
0.4375 in (11.11 mm) |
|
1/2 in |
16 |
0.5000 in (12.70 mm) |
|
9/16 in |
16 |
0.5625 in (14.29 mm) |
|
5/8 in |
14 |
0.6250 in (15.88 mm) |
|
3/4 in |
12 |
0.7500 in (19.05 mm) |
|
7/8 in |
11 |
0.8750 in (22.23 mm) |
|
1 in |
10 |
1.0000 in (25.40 mm) |
BA (British Association) Rod Sizes
BA threads are defined in millimetres, so millimetres lead here with the inch equivalent in brackets. As with Whitworth, the maximum major diameter is the nominal size, so turn the rod to the figure shown and sit a touch under.
|
Thread |
Pitch (mm) |
Major Ø (turn rod to just under) |
|---|---|---|
|
0 BA |
1.00 |
6.00 mm (0.2362 in) |
|
2 BA |
0.81 |
4.70 mm (0.1850 in) |
|
4 BA |
0.66 |
3.60 mm (0.1417 in) |
|
6 BA |
0.53 |
2.80 mm (0.1102 in) |
|
8 BA |
0.43 |
2.20 mm (0.0866 in) |
|
10 BA |
0.35 |
1.70 mm (0.0669 in) |
Die Stock Size Chart
Which die stock you need comes down to one figure: the outside diameter of your die. Circular split dies are held in split die stocks and circular solid dies are held in solid die stocks. Find your die's OD in the chart below to identify the die stock that fits it.
How to Choose the Right Die Stock
- Check your die's outside diameter: It is usually stamped on the face of the die or listed in the product specification. This is the figure the die stock is built around.
- Match the OD to the chart above: Pick the die stock whose "holds die OD" matches your die.
- Match the type: A circular split die needs a split die stock and a circular solid die needs a solid die stock. The two are not interchangeable.
A die for a given thread can be produced in more than one OD, so always work from the die's OD rather than the thread alone.
Circular Split Die Stocks (BS 1127)
Split die stocks clamp inch-OD circular split dies using three screws, which also lets you adjust the die slightly to fine-tune the thread fit.
|
Die stock size |
Holds die OD |
Die thickness |
Overall length |
|---|---|---|---|
|
13/16 in |
13/16 in (20.64 mm) |
1/4 in (6.35 mm) |
6.1/2 in |
|
1 in |
1 in (25.40 mm) |
3/8 in (9.53 mm) |
8.7/8 in |
|
1.5/16 in |
1.5/16 in (33.34 mm) |
7/16 in (11.11 mm) |
11 in |
|
1.1/2 in |
1.1/2 in (38.10 mm) |
1/2 in (12.70 mm) |
14.1/4 in |
|
2 in |
2 in (50.80 mm) |
5/8 in (15.90 mm) |
19.1/8 in |
|
2.1/4 in |
2.1/4 in (57.15 mm) |
11/16 in (17.46 mm) |
23 in |
|
3 in |
3 in (76.20 mm) |
7/8 in (22.23 mm) |
30 in |
|
4 in |
4 in (101.60 mm) |
1 in (25.40 mm) |
56 in |
Circular Solid Die Stocks (DIN 223)
Solid die stocks hold one-piece metric-OD circular dies and are sized in millimetres. Some diameters are available in more than one die thickness.
|
Die stock size |
Holds die OD |
Die thickness |
Overall length |
|---|---|---|---|
|
20 mm (0.787 in) |
20 mm (0.787 in) |
5 mm (0.197 in) or 7 mm (0.276 in) |
180 mm to 185 mm (7.09 in to 7.28 in) |
|
25 mm (0.984 in) |
25 mm (0.984 in) |
9 mm (0.354 in) |
215 mm (8.46 in) |
|
30 mm (1.181 in) |
30 mm (1.181 in) |
11 mm (0.433 in) |
270 mm (10.63 in) |
|
38 mm (1.496 in) |
38 mm (1.496 in) |
10 mm (0.394 in) or 14 mm (0.551 in) |
315 mm (12.40 in) |
|
45 mm (1.772 in) |
45 mm (1.772 in) |
14 mm (0.551 in) or 18 mm (0.709 in) |
485 mm (19.09 in) |
|
55 mm (2.165 in) |
55 mm (2.165 in) |
16 mm (0.630 in) or 22 mm (0.866 in) |
485 mm (19.09 in) |
Die Size by Thread
The thread die size chart below lists the die outside diameter most commonly supplied for each thread, so you can work back to the right die stock when you only know the thread. Dies for the same thread are sometimes produced in more than one OD, so treat these as typical sizes and confirm against the OD marked on your die.
Metric Coarse Thread Die Sizes
|
Thread |
Pitch (mm) |
Typical die OD |
Die stock |
|---|---|---|---|
|
M1.6 |
0.35 |
13/16 in (20.64 mm) |
13/16 in |
|
M2 |
0.40 |
13/16 in (20.64 mm) |
13/16 in |
|
M2.5 |
0.45 |
13/16 in (20.64 mm) |
13/16 in |
|
M3 |
0.50 |
13/16 in (20.64 mm) |
13/16 in |
|
M3.5 |
0.60 |
13/16 in (20.64 mm) |
13/16 in |
|
M4 |
0.70 |
13/16 in (20.64 mm) |
13/16 in |
|
M5 |
0.80 |
13/16 in (20.64 mm) |
13/16 in |
|
M6 |
1.00 |
13/16 in (20.64 mm) |
13/16 in |
|
M7 |
1.00 |
13/16 in (20.64 mm) |
13/16 in |
|
M8 |
1.25 |
1 in (25.40 mm) |
1 in |
|
M10 |
1.50 |
1 in (25.40 mm) |
1 in |
|
M12 |
1.75 |
1.5/16 in (33.34 mm) |
1.5/16 in |
|
M14 |
2.00 |
1.5/16 in (33.34 mm) |
1.5/16 in |
|
M16 |
2.00 |
1.1/2 in (38.10 mm) |
1.1/2 in |
|
M18 |
2.50 |
1.1/2 in (38.10 mm) |
1.1/2 in |
|
M20 |
2.50 |
2 in (50.80 mm) |
2 in |
|
M22 |
2.50 |
2 in (50.80 mm) |
2 in |
|
M24 |
3.00 |
2 in (50.80 mm) |
2 in |
Metric Fine Thread Die Sizes
A fine-pitch die uses the same OD as the coarse die of the same nominal diameter, so match on the diameter and confirm the pitch.
|
Thread |
Pitch (mm) |
Typical die OD |
Die stock |
|---|---|---|---|
|
M6 x 0.75 |
0.75 |
13/16 in (20.64 mm) |
13/16 in |
|
M8 x 1.0 |
1.00 |
1 in (25.40 mm) |
1 in |
|
M10 x 1.0 |
1.00 |
1 in (25.40 mm) |
1 in |
|
M10 x 1.25 |
1.25 |
1 in (25.40 mm) |
1 in |
|
M12 x 1.25 |
1.25 |
1.5/16 in (33.34 mm) |
1.5/16 in |
|
M12 x 1.5 |
1.50 |
1.5/16 in (33.34 mm) |
1.5/16 in |
|
M14 x 1.5 |
1.50 |
1.5/16 in (33.34 mm) |
1.5/16 in |
|
M16 x 1.5 |
1.50 |
1.1/2 in (38.10 mm) |
1.1/2 in |
|
M18 x 1.5 |
1.50 |
1.1/2 in (38.10 mm) |
1.1/2 in |
|
M20 x 1.5 |
1.50 |
2 in (50.80 mm) |
2 in |
UNC and UNF (Unified) Thread Die Sizes
|
Thread |
Typical die OD |
Die stock |
|---|---|---|
|
No. 4 (4-40 / 4-48) |
13/16 in (20.64 mm) |
13/16 in |
|
No. 6 (6-32 / 6-40) |
13/16 in (20.64 mm) |
13/16 in |
|
No. 8 (8-32 / 8-36) |
13/16 in (20.64 mm) |
13/16 in |
|
No. 10 (10-24 / 10-32) |
13/16 in (20.64 mm) |
13/16 in |
|
1/4 in (20 / 28) |
13/16 in (20.64 mm) |
13/16 in |
|
5/16 in (18 / 24) |
1 in (25.40 mm) |
1 in |
|
3/8 in (16 / 24) |
1 in (25.40 mm) |
1 in |
|
7/16 in (14 / 20) |
1.5/16 in (33.34 mm) |
1.5/16 in |
|
1/2 in (13 / 20) |
1.5/16 in (33.34 mm) |
1.5/16 in |
|
9/16 in (12 / 18) |
1.1/2 in (38.10 mm) |
1.1/2 in |
|
5/8 in (11 / 18) |
1.1/2 in (38.10 mm) |
1.1/2 in |
|
3/4 in (10 / 16) |
2 in (50.80 mm) |
2 in |
|
7/8 in (9 / 14) |
2 in (50.80 mm) |
2 in |
|
1 in (8 / 12) |
2.1/4 in (57.15 mm) |
2.1/4 in |
BSW and BSF (Whitworth) Thread Die Sizes
|
Thread |
Typical die OD |
Die stock |
|---|---|---|
|
1/8 in |
13/16 in (20.64 mm) |
13/16 in |
|
3/16 in |
13/16 in (20.64 mm) |
13/16 in |
|
1/4 in |
13/16 in (20.64 mm) |
13/16 in |
|
5/16 in |
1 in (25.40 mm) |
1 in |
|
3/8 in |
1 in (25.40 mm) |
1 in |
|
7/16 in |
1.5/16 in (33.34 mm) |
1.5/16 in |
|
1/2 in |
1.5/16 in (33.34 mm) |
1.5/16 in |
|
9/16 in |
1.1/2 in (38.10 mm) |
1.1/2 in |
|
5/8 in |
1.1/2 in (38.10 mm) |
1.1/2 in |
|
3/4 in |
2 in (50.80 mm) |
2 in |
|
7/8 in |
2 in (50.80 mm) |
2 in |
|
1 in |
2.1/4 in (57.15 mm) |
2.1/4 in |
BA (British Association) Thread Die Sizes
|
Thread |
Typical die OD |
Die stock |
|---|---|---|
|
0 BA |
13/16 in (20.64 mm) |
13/16 in |
|
2 BA |
13/16 in (20.64 mm) |
13/16 in |
|
4 BA |
13/16 in (20.64 mm) |
13/16 in |
|
6 BA |
13/16 in (20.64 mm) |
13/16 in |
|
8 BA |
13/16 in (20.64 mm) |
13/16 in |
|
10 BA |
13/16 in (20.64 mm) |
13/16 in |
FAQs
Q: What is a die stock used for?
A: A die stock, also called a die holder or die wrench, grips a circular die and gives you the leverage to turn it by hand. It is the tool that lets a thread-cutting die produce an external thread on a rod, bar or bolt.
Q: How do I know which die stock size I need?
A: Match the die stock to the outside diameter of your die, not to the thread. Check the OD stamped on the die or listed in its specification, then find that figure in the die stock size chart above.
Q: What is the difference between a split die stock and a solid die stock?
A: A split die stock holds circular split dies (the adjustable inch-OD dies made to BS 1127) and clamps them with three screws, so you can open or close the die slightly to adjust the thread fit. A solid die stock holds one-piece metric-OD dies made to DIN 223. It is best to use the corresponding die stock type with the die, for example a split die holder with a split die, but if necessary solid dies can be used in a split die holder. Some holders accommodate both types
Q: What size rod do I need to cut an external thread with a die?
A: Turn the rod to just under the nominal thread diameter, then chamfer the end to help the die start squarely. The rod size chart above gives the recommended blank diameter for efor each metric and imperial thread. A blank that is too large will bind the die and tear the thread crests, so err slightly under rather than over.
Q: Which thread standards do the dies cover?
A: The die sizes on this page cover metric coarse, metric fine and imperial threads, including UNC, UNF, BSW, BSF and BA.