ウツギ（utsugi) ; 学名：Deutzia crenata ; 英名：Crenate deutzia
Difficult to get information on the traditional use of this tree. A photographer on flicker named “autan“, added the following description on a picture he/she? took of an Utsugi blossom :
This tree used to be a very common shrub in villages, as a fence or border mark in the crop field. In spite of its popularity, this shrub has somehow seldom been planted in modern age.
The wood is thick and strong, so it has been used as a wooden nail, tooth pick or so. The leaf with its sharp edge was used to pick out the first string from a silkworm’s cocoon.
The flowers of this tree is called “U no Hana”, the flower of Uh, which is known most japanese through a song titled “The summer has come”. So this flower is generally supposed to declare the summer’s beginning. But very few urban people would be able to recognize this flower today.
[english edited from original version]
Another species called Deutzia scabra (fuzzy deutzia) is, according to The Encyclopedia Americana (1920), traditionally used by japanese joiners to polish wood, by using the leaf that’s got “stiff stellar hairs”.