Blade-Tech Industries builds the belt hardware most of the Kydex world is already drilled for. The Blade-Tech Tek-Lok and Molle-Lok are the standard upgrade when a sheath ships with a loop you can't stand, a clip that rides at the wrong angle, or no belt option at all. If you have bought a fixed blade in the last decade, there is a good chance its sheath already carries the hole pattern for one of these.
The Tek-Lok is what people mean when they say they are swapping the hardware. It is a hinged frame that clamps around the belt instead of threading onto it, so a sheath moves from a work belt to a hunting belt without unbuckling anything. Two removable shims size the channel to anything from a 1.5 inch EDC belt up to a 2.25 inch duty belt, and a rotating secondary lock sits over the primary release so it doesn't pop open when you drag a hip across a truck seat. Nine holes on a three quarter inch grid let you run the sheath vertical, horizontal, or canted. It is molded in the USA from glass filled nylon, and the design traces to a 2000 patent from Bob Terzuola and Tim Wegner.
The Molle-Lok solves the other half of the problem. It weaves through PALS channels on a plate carrier, chest rig, pack, or battle belt and locks down with a spring loaded stainless pin and metal locking bar, so the sheath stays put instead of walking around the webbing. Six holes on each side give you height options on the same three quarter inch spacing as the Tek-Lok. The small Molle-Lok suits a compact fixed blade like an ESEE riding on load bearing gear, and the large Molle-Lok spans more webbing for longer blades. Both come as a pair with screws, posts, and spacers.
Before you order, check that your sheath's holes land on the three quarter inch grid. Shopping for the sheath itself? Start with the custom work from Yellow Hawk or the fixed blades from Bradford. For deep concealment, the Blade-Tech IWB belt loops go the other direction, using a rubber band with a pull the dot snap to drop the sheath inside the waistband where a Tek-Lok would print.