🔩 Fixed Fastener Calculator
Estimate preload, tightening torque, single-shear load, and pull-out resistance for fixed fasteners in steel, wood, aluminum, and concrete connections.
📌 Job Presets
⚙ Fastener Inputs
🎯 Results
📈 Material and Spec Grid
📊 Reference Tables
| Diameter | UNC / Coarse | Tensile Area | Typical Use |
|---|---|---|---|
| 1/4 in | 20 TPI | 0.0318 in² | Panels, brackets |
| 5/16 in | 18 TPI | 0.0524 in² | Lags, stud shoes |
| 3/8 in | 16 TPI | 0.0775 in² | Anchors, machine bases |
| M8 | 1.25 mm | 36.6 mm² | Motors, guards |
| M10 | 1.50 mm | 58.0 mm² | Frames, brick anchors |
| M12 | 1.75 mm | 84.3 mm² | Column bases |
| Grade | Proof Strength | Ultimate | Target Preload |
|---|---|---|---|
| Grade 2 | 55 ksi | 74 ksi | 70% proof |
| Grade 5 | 85 ksi | 120 ksi | 75% proof |
| Grade 8 | 120 ksi | 150 ksi | 75% proof |
| A2-70 | 65 ksi | 101 ksi | 65% proof |
| 8.8 | 87 ksi | 116 ksi | 75% proof |
| 10.9 | 120 ksi | 151 ksi | 75% proof |
| Base Material | Thread / Bond | Min Engage | Edge Dist. |
|---|---|---|---|
| Carbon steel | 36 ksi shear | 1.0×D | 1.5×D |
| 6061-T6 | 18 ksi shear | 1.5×D | 2.0×D |
| SPF stud | 0.42 specific G | 8.0×D | 4.0×D |
| White oak | 0.68 specific G | 7.0×D | 5.0×D |
| 3000 psi conc. | 850 psi bond | 4.0×D | 8.0×D |
| Clay brick | 650 psi bond | 6.0×D | 10.0×D |
| Project Scenario | Fastener | Typical Torque | Notes |
|---|---|---|---|
| Stud-mounted ledger clip | 5/16 lag | 12-16 ft-lb | Need long wood embedment |
| Motor base guard | M8 8.8 | 18-22 N·m | Use flat washer both sides |
| Concrete sill bracket | 3/8 wedge | 24-30 ft-lb | Watch slab edge distance |
| Aluminum enclosure panel | 1/4-20 A2 | 6-8 ft-lb | Longer engagement helps |
| Brick equipment mount | M10 sleeve | 28-35 N·m | Capacity drops in weak units |
| Steel column base | 1/2 A325 | 55-65 ft-lb | Confirm structural spec |
💡 Shop Notes
⚠ Safety Note
This calculator helps compare fastener preload, torque, shear, and pull-out capacity in one place so you can size fixed connections with clearer thread engagement and substrate limits.
Fasteners, such as bolts, lag bolts, anchors, and inserts, hold part of a structure together. However, if a person dont understand how fasteners interact with the base material that they are securing together, the fasteners can fail. Fasteners can fail if a person does not account for preload tension, friction, shear force, and pull-out forces.
The preload tension is the initial stretch of a fastener, and tension are necessary to clamp the two parts together. If the preload tension is too low, the vibration will loosen the fastener. If the tension is too high, it may crush the material or the fastener will snap.
How Fasteners Work and Why They Fail
Torque is the rotational force use to create the preload tension, and the amount of friction that a fastener creates will determine the preload tension. The K factor for a fastener determine how much friction the fastener creates. The K factor changes based on the finish of the fastener.
Dry zinc has a K factor of 0.20, while lubricated steel have a K factor of 0.16. If a person changes the finish of a fastener, the K factor will change, and the torque will no longer accurate reflect the preload tension. Because the K factor isnt consistent, an safety margin must be added to account for this.
The base material of a fastener can hold a certain amount of load. Carbon steel holds 36 ksi in thread shear while aluminum only holds 18 ksi in thread shear. Because aluminum is softer than carbon steel, it requires 1.5 times the depth of engagement with the material.
Wood relies on specific gravity to even distribute the pull-out forces from the fastener. Spruce-pine-fir studs has a specific gravity of 0.42 while oak has a specific gravity of 0.68. This means oak will provide more resistance to the pull-out forces than spruce-pine-fir studs.
Additionally, concrete require specific calculations to even distribute the forces equally. Concrete relies on bond stress to hold the anchor in place within the concrete. The force that tries to pull the fastener out of the base material is the pull-out force.
If a person use a lag screw into a softwood structure, the embedment depth is crucial. For softwood, the embedment depth has to be eight times the diameter of the lag screw. The shear force is the force that acts in a direction perpendicular to the fastener shank.
Single shear is not as strong than the tensile strength of the material. A person must calculate the shear capacity of a fastener to ensure that the material can even distribute the lateral load. If the pull-out force is lower than the preload tension, then the embedment depth of the fastener must be increased.
In addition to the material that the fastener is securing, there are environmental factors that can impact the performance of the fasteners over time. For instance, the vibration that is present in a structure will cause the fastener to lose the preload tension, so those fasteners should be inspected after a period of time in use. The change in temperature can also impact the performance of the fasteners.
Aluminum expands and stretches twice as much as steel. Wood expands and contract based on the changes in weather seasons. Finally, a person must clean the threads of the fastener because the presence of debris will change the K factor of the fastener and make the torque reading inaccurately.
By calculating the preload tension, shear and the pull-out force of a base material, a person can ensure that the fastener will remain secure in there installation.
