Making Tiny Custom Threads for a Custom Watch Back

What's the right fit for M27x0.5 threads? I created several test pieces to try out different threads that I'll use for a custom threaded watch back. I'm using aluminum for these tests and will switch to stainless steel for the depth tests that will come soon. My Thread Calculator on Patreon: https://www.patreon.com/posts/metric-threads-74939382 Blog post with the simplified calculations: https://trains.socha.com/2022/10/metric-threads-and-tolerances.html Video on threads: https://youtu.be/wjwgINFZf7Y 00:00 Intro 00:53 Test Case and Back 03:03 Normal Fit, 6g & 6H 05:10 Custom Form Tool 06:49 Fusion CAM Simulation 08:06 Milling Test Coupons 10:50 Trying the Test Coupons 11:52 Tighter Threads 13:19 Comparing the two fits