For the rifle experts: Bolt gun safeties.

[Offfhand]

Obviusly not a bolt rifle, but on the subject of safeties, here's an interesting variation of a safety on one of my double rifles. It migh be termed a "safety safety" but more usually called a safety bolt, or block, because it prevents the safety from being disengaged. Usually found on dangerous game rifles, such as this one, the purpose is to prevent the safety from being accidently disengaged by one's gun bearer. As situation not uncommon on safari. When a shooting situation arises, the hunter, with rifle now in hand, flicks the bolter to the side so the main safety can be operated as needed.