What it is actually solving
Tile, stone, wood and vinyl all finish at different heights, and the substrates under them differ too. A bathroom floor laid in half inch stone and a hall in three eighths engineered wood do not arrive level.
The threshold takes that step and turns it into one deliberate line instead of an accident. It also gives both floors a finished edge to stop against, which matters because a cut tile edge and a cut plank end are both untidy things to leave exposed.
Length is the number that matters
These run 36 inches long, which covers a standard interior door opening with a little to spare.
The figure to measure is the full width of the opening including the jamb reveals, not the door leaf, since a threshold normally runs the whole way and gets trimmed rather than stopping short. A wider opening needs a longer piece rather than two shorter ones joined in the middle.
Four inches wide, and why
The width here is four inches, which is the common depth for an interior threshold.
It has to be wide enough to sit under the door in both its open and closed positions, so the line is never visible as a gap from either room. A narrower piece ends up with the door closing over an edge rather than over the middle of the stone.
Three quarters of an inch of solid stone
These are 3/4 inch thick, which is twice a marble field tile and is the point of the product.
A threshold is walked over more than any other square foot in a house, since every trip between two rooms crosses it. Depth is what lets it take that and what gives it enough material to be shaped where one side sits higher than the other.
Honed, in a Jerusalem limestone
The stone here is a Jerusalem limestone, honed: pale cream, fine grained and matte.
A honed surface is the sensible choice on a piece that gets walked over constantly, since a polish wears unevenly along a single narrow line far more visibly than it would across a floor. Jerusalem Light limestone covers the stone and limestone tile the material.
Saddle, threshold, transition
Three words get used for the same region and they are not quite interchangeable.
A threshold or saddle is a stone or solid piece sitting in the opening and spanning the two floors. A transition is usually a metal or vinyl profile doing the same job in a thinner section. The stone version is heavier, permanent and reads as part of the floor rather than as a fitting laid over it, which is why it turns up where the floors either side are also stone.
Where a threshold goes
Any doorway where two floors meet: bathroom to hall, kitchen to dining room, tiled entry to carpeted stair. Also the base of a shower where the pan meets the bathroom floor, which is the wettest threshold in a house.
Moldings covers the trim family and marble moldings the stone version of the other profiles.
