Friends,
I thought I would share an observation from the years of research I did for my doublegun project. On French guns of the mid-18th century it seemed that screws that were intended to be manipulated by the gun owner, like lock bolts and frizzen pivot screw, were equipped with wider slots whereas those that would generally not be manipulated by the owner were equipped with very fine slots. The cock top-jaw screw was often cut with a slot suitable for turning with a knife blade, especially low-cost guns such as fusils, but not always. The higher quality guns being more likely to have a slot for a turn-screw.
That's all I know.
Best Regards,
JMC