Spiral-threaded bolt, Part 3: Resizing and scaling the thread componentsGetting the bolt dimensions right involves both resizing and scaling operations. In this example, we're converting the standard, 1/4-inch bolt with 20 threads per inch into a 3/8-inch bolt with 16 tpi.
We start with the bolt diameter. Using the Tape Measure tool, measure the diameter of the bolt shank - 1/4 inch, by default.
Now, simply type in the new, desired diameter. In this case, we type "3/8" (again, minus the quotation marks) and hit Enter.
Unfortunately, while the bolt diameter is right, the thread pitch is not. Still, getting to 16 threads per inch is not difficult.
Use the Tape Measure tool to draw a line parallel to the bolt, starting from the top of the thread, and extending a little past the bolt.
This creates a Guide or guide line. Type 1 and Enter to resize it to 1 inch long. This should be somewhat closer to the top of the bolt than where the thread currently ends.
To resize the threaded part of the bolt only in its length - leaving its diameter unchanged - use the Scale tool. Select all thread segments, minus the Guide line.
Select the Scale tool. Hover over the various control points with your mouse until you highlight the two that will cause the selected components to rescale only in the direction of the bolt axis (the Blue axis, in this SketchUp example).
Left-click on the closer desired control point, and drag it up until the bottom of the thread lines up with the end of the Guide line. Tip: drag the control point onto the end of the Guide line, and the end of your selection should snap exactly even with this line. Release.
Congrats! You now have a perfect, 3/8" diameter, 16 tpi section of threaded bolt.