Digby Antiques (Wiltshire) has dated this piece to the 1920s.
Some can be removed easily and I think with the correct cleaning the others can all be loosened and removed. Paint brushes would have been stored in the central well.

The leather case is in excellent condition and so unusual to find this. As the case appears to have had little use it is a little difficult to fasten the buckle.
Condition of the inside is as per the photographs.
L 19 cm
W 7.5 cm
D 3.3 cm
Circa 1920’s/1030’s
Digby Antiques (Wiltshire) has dated this piece to the 1920s.
You can view the stock and full dealer information on the Digby Antiques (Wiltshire) Profile Page