Here is the solution to the problem I had with Shapr3D and bolts. I have only tested this for an M8 Bolt and plan to test it with a few other sizes. But I suspect the issue is now solved.

Here is how to create a UNC M8 x 1.25 x 16 bolt in Shapr3D.

Note: This was tested with version 3.6.1 of the app.

```
• M8 = 8 mm diameter
• 1.25 = thread pitch
• 16 = length of thread
```

To calculate the Angle in Shapr3D (number of rotations/revolve) you need to know the TPI (Threads per Inch). Since this is a metric bolt, 1” = 25.400 mm.

In this example you would divide length of thread by thread pitch to calculate the number of expected threads. (16 / 1.25 = 12.8). Based on the screenshot below you need divide the thread pitch by 2 and subtract that from the 12.8 ((1.25 / 2 = .625) → (12.8 - .625 = 12.175). So we now know that we need 12.175 threads over 16 mm for an M8 bolt.

Now to calculate the Angle in Shapr3D you multiply the new TPI (12.175) by 360 (12.175 x 360 = 4383). Now we have an angle of 4383. So in the revolve menu you would enter an angle of 4,383 and a height of 16. Anything over 4383 should not be allowed to be entered as it wouldn’t fit if you follow the math.

Now this give an exact spec bolt for the M8 example listed. Now for 3D printing I found that I had to shrink the diameter by .1 in total. So rather than a 4 mm length I had to set it to 3.95 mm before I revolve.