Most modern bolts have a round bar, held in place by ‘barrel’ hoops… the barrel bolt. The round bar, as well as sliding back and forth, can turn so the knob engages in slots to hold it in place. The ‘tower bolt’ is similar and even modern versions retain the knob that looks like the turret of fairy-tale castle
But before rolling mills could turn out miles of perfectly round bar every hour the smith had to hot-hammer a lump of iron to make a few inches, a two-man job with hammer and swage. Square was easier, so he made it square and devised an integral spring, properly tempered to stop the bar from working loose or simply falling shut or open by gravity. And that’s the basis for the Forgeries sliding boltâ€¦. in lots of shapes and sizes, pretty or purposeful, hefty or delicate but all strong enough to stand up to wear and tear, strong enough to survive where the wood they’re fixed to will give way first. Most come with an alternative ‘swan-neck’ version, with the business end offset to allow an alternative anchor point.