Nuts are designed with a specific proof load strength and thickness that when paired with the proper grade or property class of bolt, the nut will always be stronger. This is good joint design, but what precautions should be taken when designing without nuts and into blind threaded holes?
The main things you need to be concerned with when designing joints with tapped holes are material strength and thread engagement. Generally, you are stuck with a specific material, so the one variable you can change is the depth of thread engagement. Below is a rough guide take from IFI’s “Mechanical Fastening and Joining” handbook by Bengt Blendulf:
Thread Engagement Chart
| Tapped Material | 8.8/grade 5 | 10.9/grade 8 | 12.9/alloy |
| Steel, hardened | 0.8-0.9d | 0.9-1.0d | 1.0-1.3d |
| Steel, medium carbon | 0.9-1.0d | 1.0-1.2d | 1.2-1.5d |
| Steel, low carbon | 1.0-1.2d | 1.2-1.4d | – |
| Cast iron (grey) | 1.0-1.2d | 1.2-1.4d | – |
| Light alloys | 1.3-1.6d | – | – |
For more information on thread engagement, check out our technical section at www.bossard.com and try out our thread engagement calculator which is also available as an iPhone app, or contact us at ProvenProductivity@Bossard.com.
Doug Jones
Applications Engineer
Email: djones@bossard.com
