A hardwood floor transition is necessary inside doorways where rooms meet. A flooring transition presents an opportunity to change the layout direction of the individual planks without disturbing the overall flow of the hardwood floor pattern. When transitioning between rooms, you have a choice between a T-molding and what is known as a spline.
A T-molding looks like a T from its cross section. At a doorway transition point, the vertical part of the T fits in between the hardwood flooring planks of adjacent rooms. The horizontal upper portion of the T sits above the level of the hardwood floors, creating a noticeable lip or bump.
A spline does the same thing: it allows for a change in direction between rooms. A spline, however, does not sit above the level of the floor. At its cross section it looks like an oval. It fits into the facing tongues of the adjoining planks of each room, keeping them spaced apart while staying concealed beneath the floor’s level.
While the disadvantage to using T-molding is that it sticks up out of the floor, a spline can be somewhat difficult to make if done from scratch. It must fit tightly into the tongues of the adjacent boards while not causing too much separation. Both methods, however, let you change directions of the tongue and groove floor board.