Occasionally I will post pictures of a repair and someone with find it through an internet search years later and contact me with a similar problem. Here is an interesting case. The Burns gearbox truss rod adjuster has a flat blade and a special key for adjusting the neck at the heel of the guitar. The access is a hole is deep and if the blade breaks off there is no way to adjust the neck.
The first time I did this repair I only had a small Sherline lathe and I didn’t have the ability to broach a hexagonal hole. I have since acquired several larger lathes and built a broaching tool so instead of making a slot for adjusting with a flat screwdriver I was able to broach a 5/16 hex hole for adjusting with a hex wrench.