I need help identifying a bolt thread. The hardware store is closed and the only tool I have is a ruler.
It is possible to identify a bolt thread with just a ruler, by measuring the distance between threads and the diameter of the bolt shank. To do this, you'll need to measure the following:

Pitch: This is the distance from one thread crest to the next, in millimeters. You can measure this by using a ruler to count the number of threads in a 25mm length and divide by 25.

Diameter: This is the distance from one side of the bolt shank to the other, in millimeters. You can measure this by using a ruler to measure the widest part of the shank.

Once you have these measurements, you can compare them to a thread pitch chart, which can be found online. This will help you identify the thread size and type (e.g., metric, UNF, UNC, etc.).

It is worth mentioning that measuring thread pitch with just a ruler can be difficult and may not be accurate, especially with worn or damaged threads. If you can, it is best to use a thread pitch gauge or caliper for a more accurate measurement.
Can you give me a step-by-step walkthrough of the process?
Sure, here's a step-by-step process to identify a bolt thread using a ruler:

1. Clean the bolt: Make sure the bolt is free of dirt, grease, and other debris so that your measurements are accurate.

2. Measure the pitch: Place the ruler on the flat of the thread, zeroing it on the crest of one thread. Measure the distance to the crest of the adjacent thread. This measurement is the pitch of the thread.

3. Measure the diameter: Use a ruler to measure the distance across the flat of the bolt head or the shank immediately under the head. This measurement is the diameter of the bolt.

4. Use the measurements to find the bolt thread size: The measurements of the pitch and diameter can be used to find the specifications of the bolt and its thread size. There are standard thread sizes for bolts, and you can use charts or online resources to match your measurements to a thread size.

5. Verify the thread size: To confirm the thread size, try threading a nut onto the bolt. If the nut threads on easily and fits tightly, your measurements are correct and you have successfully identified the thread size.

Note: If you don't have a ruler, you can estimate the pitch by counting the number of threads in a one-inch length of the bolt and dividing by the number of threads.