Shikii is a long piece of timber laid between pillars, which functions as a threshold with grooves for sliding doors and shoji screens.
While shikii means the bottom part of the threshold, the upper part is called “kamoi”. They are used together as a pair.
The word, shikii, is derived from an ancient word, shikimi. A timber is carved to create grooves or to be fitted with a rail for shoji screens or fusuma sliding doors that partition off rooms.  For other sliding doors used for front and back entrances or windows, various methods are used to ensure smoother sliding.
The strength and smooth sliding surface is key to choosing materials, and the pine tree is generally used for shikii. Japanese hemlock, cherry tree and hinoki cypress tree are also favorably used.
In recent years, as buildings become more “barrier free”, in order to prevent disabled people and senior citizens from tripping on shikii, an increasing number of residences are eliminating difference in levels in a house by taking such measures as burying shikii under the floor.
Shikii create a sense of boundaries within space which is a very elemental concept of Japanese traditional architecture.