1/4th in bolt centerer

thingiverse

To practice drilling bolts before investing in metric ones, attempt making a hotend using a 1/4th bolt. However, without professional tools like a metal lathe, the process can be challenging with just a hand drill. To achieve success, insert a 626zz bearing into the bolt and secure it with two nuts on the end to prevent wobbling. Use a drill bit that fits the center of the bearing and drill slowly without applying excessive pressure; this will create a cone in the center of the bolt if everything is leveled correctly. With this technique, you can achieve decent accuracy when drilling through the bolt with a hand drill.