MECHANICAL FASTENERS
General
Mechanical parts shall be assembled in accordance with the requirements described herein unless otherwise specified in the applicable product documentation.
Threaded Hardware Damage
Extreme care shall be exercised during the assembly of threaded parts to avoid cross-threading or deformation.
Cross-Threading
Usually the result of attempted use of mismatched threaded parts, or improper thread starting followed by extreme force.
Deformation
Usually caused by not using the correct tool to tighten or through exertion of excessive force.
Assembly Sequence General Application
Flat washers shall always be installed between the nut and the surface of items assembled. A flat washer shall also be installed between the screw head and the surface of items assembled where those surfaces are either non-metallic of compressible material, painted or in any combination thereof.
Lock washers are available as "split lock", "Internal tooth" and "external tooth" types. Internal tooth washers are used for small head screws such as Fillister head or Cap screws; external tooth type is for use under large head screws such as Binder head screws. Any of the three types are acceptable for use with Pan Head screws. Lock washers shall be used under the heads of all screws employed in tapped holes, with the exception of Flathead screws used at countersunk hole applications, or where self-locking screws are employed.
Self Locking Hardware
Both screws and nuts are available with built-in locking features. Use of this type of hardware eliminates the need for lock washers or for the liquid staking compound described in Self-locking nuts and screws shall not be used together.
Nut - Available in "all metal" or "plastic insert" types.
The all metal types obtain their locking action through screw thread engagement in a deformed section of the nut. The plastic insert types (Elastic Stop Nut) exert a friction grip on the screw threads upon insertion. Neither type is reusable. Screw - As with the "elastic stop nut", a plastic insert provides the locking action. Proper usage requires that the mating thread part include an entrance chamfer to prevent shearing of the insert as it enters the first thread.
Staking Liquid
Liquid staking compounds, which are used to ensure mechanical fastener reliability, shall be employed only when use of mechanical locking devices, such as lock washers, self-locking nuts, or screws, is not practical. This staking compound, which is commonly referred to by its "brand name" (Loctite) is available in several types.
Thread Protrusion
Screws shall extend beyond nut or threaded surface by a minimum of 1 1/2 thread unless otherwise specified in applicable drawing.
Screws entering blind holes shall engage threads for a minimum depth equivalent to 1 1/2 times the screw diameter. This shall apply to self-tapping screws or screws entering tapped holes.
Tightness/Torque
Threaded products achieve their holding power from the tension, or twisting force, derived during the mating of the external and internal threads. Therefore, all screws shall be tightened to the degree necessary to assure the proper holding power. This assurance is provided by applying torque in accordance with the values specified in the table below. The torque limits are expressed in "inch pounds.
BOLT THREAD SIZE | Stainless Steel | Brass | Silicone Bronce | Aluminum | Monel | |||||
| MIN | MAX | MIN | MAX | MIN | MAX | MIN | MAX | MIN | MAX |
2-56 | 2.0 | 3.0 | 1.5 | 2.5 | 2.0 | 2.5 | 1.0 | 2.0 | 2.0 | 3.0 |
3-56 | 4.0 | 5.0 | 3.0 | 4.0 | 3.5 | 4.5 | 2.0 | 2.5 | 4.0 | 5.0 |
4-40 | 4.0 | 6.0 | 4.0 | 5.0 | 4.5 | 5.5 | 2.5 | 3.0 | 5.0 | 6.0 |
6-32 | 9.0 | 11.0 | 7.0 | 9.0 | 8.0 | 10.0 | 5.0 | 6.0 | 9.0 | 11.0 |
8-32 | 18.0 | 22.0 | 14.0 | 18.0 | 16.5 | 20.0 | 10.0 | 12.0 | 18.0 | 22.0 |
10-32 | 29.0 | 35.5 | 23.0 | 28.5 | 26.0 | 32.0 | 17.0 | 21.0 | 31.0 | 38.0 |
1/4-20 | 70.0 | 84.0 | 55.0 | 68.0 | 62.0 | 76.0 | 41.0 | 50.0 | 77.0 | 94.0 |
Special Applications
Truss head Screw
This type of screw has a head of much greater diameter than standard hardware of the same size, making it ideally suited for use in elongated holes. Unless installed through a painted surface, trusshead screws will not require use of a flat washer under the head.
Flathead Screw
This type of screw is used where the projection of standard hardware head would interfere at higher assembly levels.
Self-Tapping/Thread Rolling Screws
Application for these types should be limited to small gauge sheet metal and/or where frequent disassembly and re-assembly will not be required.
Chips formed by the thread-cutting action shall be removed to preclude their entry into undesirable areas.
Re-use of holes, once threads have been formed by screw reinstallation, is permitted if screw used can be fully tightened within specification.
Eyelets & Rivets
Eyelets and rivets are used to fasten two or more mechanical parts together, often providing an alternative to screw/washer/nut assembly.
Eyelet and Rivet Selection Eyelets
The recommended protrusion length through the mounting surfaces shown in the table below are provided only as a guide; sample settings should be made and qualified for each new application.
RIVET SELECTION CHART
REGULAR PACK |
INDUSTRIAL PACK |
BULK PACK |
DESCRIPTION |
HOLE RIVET DIAMETER |
RIVET GRIP RANGE | |||
ITEM NO. |
QTY |
ITEM NO. |
QTY |
ITEM NO. |
QTY | |||
RSA1/8 |
25 |
RSA1/8IP |
100 |
RSA1/8BP |
500 |
SHORT ALUMINUM RIVET |
1/8" |
1/8" |
RMA1/8 |
20 |
RMA1/8IP |
100 |
RMA1/8BP |
500 |
MEDIUM ALUMINUM RIVET |
1/8" |
1/4" |
RLA1/8 |
15 |
RLA1/8IP |
100 |
RLA1/8BP |
500 |
LONG ALUMINUM RIVET |
1/8" |
1/2" |
RSS1/8 |
25 |
RSS1/8IP |
100 |
RSS1/8BP |
500 |
SHORT STEEL RIVET |
1/8" |
1/8" |
RMS1/8 |
20 |
RMS1/8IP |
100 |
RMS1/8BP |
500 |
MEDIUM STEEL RIVET |
1/8" |
1/4" |
RLS1/8 |
15 |
RLS1/8IP |
100 |
|
|
LONG STEEL RIVET |
1/8" |
1/2" |
RSA5/32 |
20 |
RSA5/32IP |
50 |
RSA5/32BP |
500 |
SHORT ALUMINIUM RIVET |
5/32" |
1/8" |
RMA5/32 |
20 |
RMA5/32IP |
50 |
RMA5/32BP |
500 |
MEDIUM ALUMINUM RIVET |
5/32" |
1/4" |
RLA5/32 |
15 |
RLA5/32IP |
50 |
|
|
LONG ALUMINUM RIVET |
5/32" |
1/2" |
RSA3/16 |
18 |
RSA3/16IP |
50 |
|
|
SHORT ALUMINUM RIVET |
3/16" |
1/8" |
RMA3/16 |
15 |
RMA3/16IP |
50 |
RMA3/16BP |
250 |
MEDIUM ALUMINUM RIVET |
3/16" |
1/4" |
RLA3/16 |
12 |
RLA3/16IP |
50 |
RLA3/16BP |
250 |
LONG ALUMNINUM RIVET |
3/16" |
1/2" |
RSAW1/8 |
25 |
RSAW1/8IP |
100 |
RSAW1/8BP |
500 |
SHORT ALUMINUM RIVET WHITE |
1/8" |
1/8" |
RSST1/8 |
25 |
|
|
|
|
SHORT STAINLESS STEEL RIVET |
1/8" |
1/8" |
RMST1/8 |
20 |
|
|
|
|
MEDIUM STAINLESS STEEL RIVET |
1/8" |
1/4" |
RLST1/8 |
15 |
|
|
|
|
LONG STAINLESS STEEL RIVET |
1/8" |
1/2" |
RSST5/32 |
15 |
|
|
|
|
SHORT STAINLESS STEEL RIVET |
5/32" |
1/8" |
RMST5/32 |
15 |
|
|
|
|
MEDIUM STAINLESS STEEL RIVET |
5/32" |
1/4" |
WA1/8 |
30 |
|
|
WA1/8BP |
500 |
ALUMINUM WASHER |
1/8" |
|
WA3/16 |
30 |
|
|
WA3/16BP |
500 |
ALUMINUM WASHER |
3/16" |
|
WS1/8 |
40 |
|
|
|
|
STEEL WASHER |
1/8" |
|
Rivets
Recommended minimum "clinch allowances" are shown in the table below. To determine rivet length to be used for a given application, add combined thicknesses of materials to be joined and the clinch allowance or grip range dimension shown, then use the next higher applicable increment.
Acceptance Criteria
Eyelets and rivets shall be formed and shall firmly secure the joined parts. Looseness, which permits a separation of the joined parts, shall be considered cause for rejection.
Excessively tight installation usually results in damage to either the fastener or to the surface of the joined parts.
Up to three splits are permitted at either end of the fastener unless extension into the barrel portion is noted.
No circumferential split or cracks are permitted.
Damage, such as evidence of delaminating on epoxy-glass board material shall not extend more than 0.030" from the rivet or eyelet periphery.
ASTM, SAE AND ISO GRADE MARKINGS AND MECHANICAL PROPERTIES FOR STEEL FASTENERS
Identification | Specification | Fastener | Material | Nominal Size | Mechanical Properties | ||
Proof Load | Yield Strength | Tensile Strength | |||||
| SAE J429 | Bolts, | Low or Medium Carbon Steel | 1/4 thru 1-1/2 | 33,000 | 36,000 | 60,000 |
ASTM A307 | Low Carbon Steel | 1/4 thru 4 | -- | -- | |||
SAE J429 | Low or Medium Carbon Steel | 1/4 thru 3/4 Over 3/4 to 1-1/2 | 55,000 | 57,000 | 74,000 | ||
| SAE J429 | Studs | Medium Carbon Cold Drawn Steel | 1/4 thru 1-1/2 | -- | 100,000 | 115,000 |
| ASTM A193 | | AISI 501 | 1/4 Thru 4 | -- | 80,000 | 100,000 |
| ASTM A193 | AISI 410 | 85,000 | 110,000 | |||
| ASTM A193 | AISI 4140, 4142, OR 4105 | 1/4 thru 2-1/2 | -- | 105,000 | 125,000 | |
| ASTM A193 | CrMoVa Alloy Steel | 105,000 | 125,000 | |||
| ASTM A193 | AISI 304 | 1/4 and larger | -- | 30,000 | 75,000 | |
| ASTM A193 | AISI 347 | |||||
| ASTM A193 | AISI 316 | |||||
| ASTM A193 | Bolts, | AISI 321 | 1/4 and larger | -- | 30,000 | 75,000 |
| ASTM A193 | AISI 304 | 1/4 thr 3/4 | -- | 100,000 | 125,000 | |
| ASTM A193 | AISI 347 | |||||
| ASTM A193 | AISI 316 | 95,000 | 110,000 | |||
| ASTM A193 | AISI 321 | 100,000 | 125,000 | |||
| ASTM A320 | Bolts, | AISI 4140, | 1/4 thru 2-1/2 | -- | 105,000 | 125,000 |
| ASTM A320 | AISI 4037 | |||||
| ASTM A320 | AISI 4137 | |||||
| ASTM A320 | AISI 8740 | |||||
| ASTM A320 | AISI 4340 | 1/4 thru 4 | -- | 105,000 | 125,000 | |
| ASTM A320 | Bolts, | AISI 304 | 1/4 and larger | -- | 30,000 | 75,000 |
| ASTM A320 | AISI 347 | |||||
| ASTM A320 | AISI 321 | |||||
| ASTM A320 | AISI 303 | |||||
| ASTM A320 | AISI 316 | |||||
| ASTM A320 | AISI 304 | 1/4 thru 3/4 | -- | 100,000 | 100,000 | |
| ASTM A320 | AISI 347 | |||||
| ASTM A320 | AISI 303 | |||||
| ASTM A320 | AISI 316 | |||||
| ASTM A320 | AISI 321 | |||||
SAE J429 | Bolts, | Medium Carbon Steel, Quenched and Tempered | 1/4 thru 1 | 85,000 | 92,000 | 120,000 | |
ASTM A449 | 1/4 thru 1 | 85,000 | 92,000 | 120,000 | |||
SAE J429 | Sems | Low or Medium Carbon Steel, Quenched and Tempered | No. 6 | 85,000 | -- | 120,000 | |
SAE J429 | Bolts, | Low Carbon Martensitic Steel, Quenched and Tempered | 1/4 thru 1 | 85,000 | 92,000 | 120,000 | |
| ASTM A325 | High Strength | Medium Carbon Steel, Quenched and Tempered | 1/2 thru 1 | 85,000 | 92,000 | 120,000 |
| ASTM A325 | Low Carbon Martensitic Steel, Quenched and Tempered | 1/2 thru 1 | 85,000 | 92,000 | 120,000 | |
| ASTM A325 | Atmospheric Corrosion Resisting Steel, Quenched and Tempered | 1/2 thru 1 | 85,000 | 92,000 | 120,000 | |
| ASTM A354 | Bolts, | Alloy Steel, Quenched and Tempered | 1/4 thru 2-1/2 | 80,000 | 83,000 | 105,000 |
| ASTM A354 | 105,000 | 109,000 | 125,000 | |||
SAE J429 | Bolts, | Medium Carbon Alloy Steel, Quenched and Tempered 4 | 1/4 thru 1-1/2 | 105,000 | 115,000 | 133,000 | |
SAE J429 | Bolts, | Medium Carbon Alloy Steel, Quenched and Tempered | 1/4 thru 1-1/2 | 120,000 | 130,000 | 150,000 | |
ASTM A354 | Alloy Steel, Quenched and Tempered 4 | ||||||
| SAE J429 | Studs | Medium Carbon Alloy or SAE 1041 Modified Elevated Temperature Drawn Steel | 1/4 thru 1-1/2 | 120,000 | 130,000 | 150,000 |
| ASTM A490 | High Strength Structural Bolts | Alloy Steel, Quenched and Tempered | 1/2 thru 1-1/2 | 120,000 | 130,000 | 150,000 min |
| ISO R898 | Bolts, | Medium Carbon Steel, Quenched and Tempered | All Sizes | 33,000 | 36,000 | 60,000 |
| ISO R898 | 55,000 | 57,000 | 74,000 | |||
8.8 | ISO R898 | Alloy Steel, Quenched and Tempered | 85,000 | 92,000 | 120,000 | ||
10.9 | ISO R898 | 120,000 | 130,000 | 150,000 | |||
FASTENER IDENTIFICATION MARKING
Grade | Specification | Material | Nominal Size | Proof | Hardness | See | |
Min | Max | ||||||
| ASTM A563 - Grade 0 | Carbon Steel | 1/4 thru 1-1/2 | 69 | B55 | C32 | 3,4 |
ASTM A563 - Grade A | Carbon Steel | 1/4 thru 1-1/2 | 90 | B68 | C32 | 3,4 | |
ASTM A563 - Grade B | Carbon Steel | 1/4 thru 1 | 120 | B69 | C32 | 3,4 | |
over 1 thru 1-1/2 | 105 | ||||||
ASTM A563 - Grade C | Carbon Steel | 1/4 thru 4 | 144 | B78 | C38 | 5 | |
ASTM A563 - Grade C3 | Atmospheric | 1/4 thru 4 | 144 | B78 | C38 | 5,9 | |
ASTM A563 - Grade D | Carbon Steel | 1/4 thru 4 | 150 | B84 | C38 | 6 | |
ASTM A563 - Grade DH | Carbon Steel | 1/4 thru 4 | 175 | C24 | C38 | 6 | |
ASTM A563 - Grade DH3 | Atmospheric | 1/4 thru 4 | 175 | C24 | C38 | 5,9 | |
ASTM A194 - Grade 1 | Carbon Steel | 1/4 thru 4 | 130 | B70 | -- | 7 | |
ASTM A194 - Grade 2 | Medium Carbon | 1/4 thru 4 | 150 | 159 | 352 | 7,8 | |
ASTM A194 - Grade 2H | Medium Carbon | 1/4 thru 4 | 175 | C24 | C38 | 7 | |
ASTM A194 - Grade 2HM | Medium Carbon | 1/4 thru 4 | 150 | 159 | 237 | 7,8 | |
ASTM A194 - Grade 4 | Medium Carbon | 1/4 thru 4 | 175 | C24 | C38 | 7 | |
ASTM A194 - Grade 7 | Medium Carbon | 1/4 thru 4 | 175 | C24 | C38 | 7 | |
ASTM A194 - Grade 7M | Medium Carbon | 1/4 thru 4 | 150 | 159 | 237 | 7 | |
See Note 1,2 | 10 | | | | | | |
NOTES:
- In addition to the indicated grade marking, all grades, except A563 grades O, A and B, must be marked for manufacturer identification.
- The markings shown for all grades of A194 nuts are for cold formed and hot forged nuts. When nuts are machined from bar stock the nut must be additionally marked with the letter 'B'.
- Nuts are not required to be marked unless specified by the purchaser. When marked, the identification marking shall be the grade letter O, A or B.
- Properties shown are those of nonplated or noncoated coarse thread hex nuts.
- Properties shown are those of coarse thread heavy hex nuts.
- Properties shown are those of coarse thread heavy hex nuts.
- Properties shown are those of coarse 8-pitch thread heavy hex nuts.
- Hardnesses are Brinell Hardness Numbers.
- The nut manufacturer, at his option, may add other markings to indicate the use of atmospheric corrosion resistant steel.
- Specifications --
ASTM A563 -- Carbon and Alloy Steel Nuts.
ASTM A194/A194M -- Carbon and Alloy Steel Nuts for Bolts for High Pressure and High Temperature Service.