Boat Rules of Thumb
Bolt Strength
|
Coarse Thread Series - UNC |
Fine Thread Series - UNF |
|
Nominal Size and Threads Per In. |
Basic Pitch Dia. |
Section at Minor Dia. |
Tensile Stress Area |
Nominal Size and Threads Per In. |
Basic Pitch Dia. |
Section at Minor Dia. |
Tensile Stress Area |
|
In. |
Sq in. |
Sq in. |
In. |
Sq in. |
Sq in. |
|
-- -- |
-- |
-- |
-- |
0 - 80 |
0.0519 |
0.00151 |
0.00180 |
|
1 - 64 |
0.0629 |
0.00218 |
0.00263 |
1 - 72 |
0.0640 |
0.00237 |
0.00278 |
|
2 - 56 |
0.0744 |
0.00310 |
0.00370 |
2 - 64 |
0.0759 |
0.00339 |
0.00394 |
|
3 - 48 |
0.0855 |
0.00406 |
0.00487 |
3 - 56 |
0.0874 |
0.00451 |
0.00523 |
|
4 - 40 |
0.0958 |
0.00496 |
0.00604 |
4 - 48 |
0.0985 |
0.00566 |
0.00661 |
|
5 - 40 |
0.1088 |
0.00672 |
0.00796 |
5 - 44 |
0.1102 |
0.00716 |
0.00830 |
|
6 - 32 |
0.1177 |
0.00745 |
0.00909 |
6 - 40 |
0.1218 |
0.00874 |
0.01015 |
|
8 - 32 |
0.1437 |
0.01196 |
0.0140 |
8 - 36 |
0.1460 |
0.01285 |
0.01474 |
|
10 - 24 |
0.1629 |
0.01450 |
0.0175 |
10 - 32 |
0.1697 |
0.0175 |
0.0200 |
|
12 - 24 |
0.1889 |
0.0206 |
0.0242 |
12 - 28 |
0.1928 |
0.0226 |
0.0258 |
|
1/4 - 20 |
0.2175 |
0.0269 |
0.0318 |
1/4 - 28 |
0.2268 |
0.0326 |
0.0364 |
|
5/16 - 18 |
0.2764 |
0.0454 |
0.0524 |
5/16 - 24 |
0.2854 |
0.0524 |
0.0580 |
|
3/8 - 16 |
0.3344 |
0.0678 |
0.0775 |
3/8 - 24 |
0.3479 |
0.0809 |
0.0878 |
|
7/16 - 14 |
0.3911 |
0.0933 |
0.1063 |
7/16 - 20 |
0.4050 |
0.1090 |
0.1187 |
|
1/2 - 13 |
0.4500 |
0.1257 |
0.1419 |
1/2 - 20 |
0.4675 |
0.1486 |
0.1599 |
|
9/16 - 12 |
0.5084 |
0.162 |
0.182 |
9/16 - 18 |
0.5264 |
0.189 |
0.203 |
|
5/8 - 11 |
0.5660 |
0.202 |
0.226 |
5/8 - 18 |
0.5889 |
0.240 |
0.256 |
|
3/4 - 10 |
0.6850 |
0.302 |
0.334 |
3/4 - 16 |
0.7094 |
0.351 |
0.373 |
|
7/8 - 9 |
0.8028 |
0.419 |
0.462 |
7/8 - 14 |
0.8286 |
0.180 |
0.509 |
|
1 - 8 |
0.9188 |
0.551 |
0.606 |
1 - 12 |
0.9459 |
0.625 |
0.663 |
|
1-1/8 - 7 |
1.0322 |
0.693 |
0.763 |
1-1/8 - 12 |
1.0709 |
0.812 |
0.856 |
|
1-1/4 - 7 |
1.1572 |
0.890 |
0.969 |
1-1/4 - 12 |
1.1959 |
1.024 |
1.073 |
|
1-3/8 - 6 |
1.2667 |
1.054 |
1.155 |
1-3/8 - 12 |
1.3209 |
1.260 |
1.315 |
|
1-1/2 - 6 |
1.3917 |
1.294 |
1.405 |
1-1/2 - 12 |
1.4459 |
1.521 |
1.581 |
|
-- -- |
-- |
-- |
-- |
-- -- |
-- |
-- |
-- |
|
1-3/4 - 5 |
1.6201 |
1.74 |
1.90 |
-- -- |
-- |
-- |
-- |
|
-- -- |
-- |
-- |
-- |
-- -- |
-- |
-- |
-- |
|
2 - 4-1/2 |
1.8557 |
2.30 |
2.50 |
-- -- |
-- |
-- |
-- |
|
2-¼ - 4-½ |
2.1057 |
3.02 |
3.25 |
-- -- |
-- |
-- |
-- |
|
2-1/2 - 4 |
2.3376 |
3.72 |
4.00 |
-- -- |
-- |
-- |
-- |
|
2-3/4 - 4 |
2.5876 |
4.62 |
4.93 |
-- -- |
-- |
-- |
-- |
|
3 - 4 |
2.8376 |
5.62 |
5.97 |
-- -- |
-- |
-- |
-- |
|
3-1/4 - 4 |
3.0876 |
6.72 |
7.10 |
-- -- |
-- |
-- |
-- |
|
3-1/2 - 4 |
3.3376 |
7.92 |
8.33 |
-- -- |
-- |
-- |
-- |
|
3-3/4 - 4 |
3.5876 |
9.21 |
9.66 |
-- -- |
-- |
-- |
-- |
|
4 - 4 |
3.8376 |
10.61 |
11.08 |
-- -- |
-- |
-- |
-- |
|
STEP 1
The strength of a bolt depends partly on it's cross section, or
that area of solid metal. The area of a 3/8" bolt is not same
as the area of a 3/8" circle so the Pi R^2 or 3.142x(0.375/2 )^2
= 0.110 square inches is actually too large because the area is
reduced by the threads. A 3/8", 16 threads per inch, course
thread bolt has a minimum cross section of 0.0678" and the
same diametet bolt in 24 threads per inch, fine tread has a minimum
cross section of 0.0809". So fine thread bolts are
stronger, except they need a little more length of threads that are
engaged in order to make up for having slightly weaker threads.
The chart list cross sections for various standard bolts.
STEP 2
Select a metal that is the same metal as what you are bolting
together or as close as possible on the galvanic series chart.
When two dissimilar metals are in contact, especially in sea water,
the anode metal or the metal with the more negative charge will
corrode to the cathode metal with the more positive charge.
The different in charges between the two metals should be no more
that .15 volts if possible.
The chart list Alloys in the order of the potential they in
flowing sea water. Certain alloys like Stainless Steel 410 have a
potential near -0.5 volts when they are in low velocity or poorly
aerated water. This range is marked in black.
For example our prop blades are cast from NiBrAl or
Nickel-Aluminum Bronze which is -.02. Those blades are bolted
to the NiBrAl hub with Stainless Steel 410 at -.02 except when in
brackish water when it might be a -.05 Either way, they are
close enough.
STEP 3
Once you know the type of metal for the bolt, you look up it's
yield strength which is commonly expressed in psi. From Step 1 you
know the area of the bolt so you can multiply that area by the psi.
For example a 410-HT grade stainless bolt has a yield strength of
135,000 psi. A 3/8" fine treaded
bolt has an area of 0.0809, so 0.0809 x 135,000 = 10,921.5 pounds.
A safe load is about half the yield strength so call it 5000 pounds.
|
Grade(1) |
General
Descpription
of Material |
Bolts, Screws and Studs |
Nuts |
Full
Size Bolts,
Screws, Studs |
Machine Test Sprecimens of
Bolts, Screws, Studs |
Proof
Load
Stress |
Yield (2)
Strength |
Tensile
Strength |
Yield (2)
Strength |
Tensile
Strength |
Elong-
ation(3) |
|
Min
psi |
Min
psi |
Min
psi |
Min
psi |
%
Min. |
psi |
|
303A |
Austenitic
Stainless Steel-
Sol. Annealed |
30,000 |
75,000 |
30,000 |
75,000 |
20 |
75,000 |
|
304-A |
Austenitic
Stainless Steel-
Sol. Annealed |
30,000 |
75,000 |
30,000 |
75,000 |
20 |
75,000 |
|
304 |
Austenitic
Stainless Steel-
Cold Worked |
50,000 |
90,000 |
45,000 |
85,000 |
20 |
90,000 |
|
304-SH |
Austenitic
Stainless Steel-
Strain Hardened |
See
Note 6 |
See
Note 6 |
See
Note 6 |
See
Note 6 |
15 |
See
Note 6 |
|
305-A |
Austenitic
Stainless Steel-
Sol. Annealed |
30,000 |
75,000 |
30,000 |
75,000 |
20 |
75,000 |
|
305 |
Austenitic
Stainless Steel-
Cold Worked |
50,000 |
90,000 |
45,000 |
85,000 |
20 |
90,000 |
|
305-SH |
Austenitic
Stainless Steel-
Strain Hardened |
See
Note 6 |
See
Note 6 |
See
Note 6 |
See
Note 6 |
15 |
See
Note 6 |
|
316-A |
Austenitic
Stainless Steel-
Sol. Annealed |
30,000 |
75,000 |
30,000 |
75,000 |
20 |
75,000 |
|
316 |
Austenitic
Stainless Steel-
Cold Worked |
50,000 |
90,000 |
45,000 |
85,000 |
20 |
90,000 |
|
316-SH |
Austenitic
Stainless Steel-
Strain Hardened |
See
Note 6 |
See
Note 6 |
See
Note 6 |
See
Note 6 |
15 |
See
Note 6 |
|
XM7-A |
Austenitic
Stainless Steel-
Sol. Annealed |
30,000 |
75,000 |
30,000 |
75,000 |
20 |
75,000 |
|
XM7 |
Austenitic
Stainless Steel-
Cold Worked |
50,000 |
90,000 |
45,000 |
85,000 |
20 |
90,000 |
|
384-A |
Austenitic
Stainless Steel-
Sol. Annealed |
30,000 |
75,000 |
30,000 |
75,000 |
20 |
75,000 |
|
384 |
Austenitic
Stainless Steel-
Cold Worked |
50,000 |
90,000 |
45,000 |
85,000 |
20 |
90,000 |
|
410-H |
Martensitic
Stainless Steel-
Hardened and
Tempered |
95,000 |
125,000 |
95,000 |
125,000 |
20 |
125,000 |
|
410-HT |
Martensitic
Stainless Steel-
Hardened and
Tempered |
135,000 |
180,000 |
135,000 |
180,000 |
12 |
180,000 |
|
416-H |
Martensitic
Stainless Steel-
Hardened and
Tempered |
95,000 |
125,000 |
95,000 |
125,000 |
20 |
125,000 |
|
416-HT |
Martensitic
Stainless Steel-
Hardened and
Tempered |
135,000 |
180,000 |
135,000 |
180,000 |
12 |
180,000 |
|
430 |
Ferritic
Stainless Steel |
40,000 |
70,000 |
40,000 |
70,000 |
20 |
70,000 |
|
464-HF |
Naval Brass |
15,000 |
52,000 |
14,000 |
50,000 |
25 |
52,000 |
|
464 |
Naval Brass |
27,000 |
60,000 |
25,000 |
57,000 |
25 |
60,000 |
|
462 |
Naval Brass |
27,000 |
52,000 |
24,000 |
50,000 |
20 |
52,000 |
|
642 |
Aluminum
Bronze |
35,000 |
72,000 |
35,000 |
72,000 |
15 |
72,000 |
|
630 |
Aluminum
Bronze |
50,000 |
105,000 |
50,000 |
105,000 |
10 |
105,000 |
|
614 |
Aluminum
Bronze |
40,000 |
75,000 |
40,000 |
75,000 |
30 |
75,000 |
|
510 |
Phosphor
Bronze |
35,000 |
60,000 |
35,000 |
60,000 |
15 |
60,000 |
|
675 |
Manganese
Bronze |
22,000 |
55,000 |
22,000 |
55,000 |
20 |
55,000 |
|
655-HF |
Silicon
Bronze |
20,000 |
52,000 |
18,500 |
50,000 |
20 |
52,000 |
|
655 |
Silicon
Bronze |
38,000 |
70,000 |
36,000 |
68,000 |
15 |
70,000 |
|
651 |
Silicon
Bronze |
45,000 |
75,000 |
42,500 |
72,000 |
8 |
75,000 |
|
661 |
Silicon
Bronze |
38,000 |
70,000 |
38,000 |
70,000 |
15 |
70,000 |
NICU-
A-HF |
Nickel-Copper
Alloy A |
25,000 |
70,000 |
25,000 |
70,000 |
20 |
70,000 |
|
NICU-A |
Nickel-Copper
Alloy A |
40,000 |
80,000 |
40,000 |
80,000 |
20 |
80,000 |
|
NICU-B |
Nickel-Copper
Alloy B |
40,000 |
80,000 |
40,000 |
80,000 |
20 |
80,000 |
|
NICU-K(7) |
Nickel-Copper
Aluminum Alloy |
90,000 |
130,000 |
90,000 |
130,000 |
20 |
130,000 |
|
2024-T4 |
Aluminum
Alloy |
40,000 |
55,000 |
40,000 |
55,000 |
14 |
55,000 |
|
6061-T6 |
Aluminum
Alloy |
35,000 |
42,000 |
35,000 |
42,000 |
12 |
42,000 |
Note 6. Austenitic stainless steel, strain
hardened bolts, screws, studs, and nuts
have the following strength per properties.
Product
Size |
Bolts, Screws, Studs |
Nuts |
|
Tested Full Size |
Machine Test Specimens, |
Proof
Load
Stress |
Yield
Strength |
Tensile
Strength |
Yield
Strength |
Tensile
Strength |
|
in. |
min
psi |
min
psi |
min
psi |
min
psi |
psi |
|
to 5/8 in. |
100,000 |
125,000 |
90,000 |
115,000 |
125,000 |
|
over 5/8 to
1 in. |
70,000 |
105,000 |
65,000 |
100,000 |
105,000 |
|
over 1 to
1-1/2 in. |
50,000 |
90,000 |
45,000 |
85,000 |
90,000 |
|
|
|
