It is extremely nice to be able to use a caliper to measure screw/bolt major diameter (and length) to find correct replacements. However I am struggling to come up with a good way to determine accurate threads per inch (TPI; eyeball counts are difficult for me to get right, especially for smaller screws/etc).
What would folks here recommend for accurately determining TPI? I would prefer something other than prebuilt thread gauges, which based on my research are relatively expensive, dedicated-use, and of surprisingly variant build quality/accuracy (e.g., folks have complained about such gauges not being tapped correctly!!!). Thanks for any advice.