The top right is a hand holding a brush on the left.
Let us compare it with 書 - Write (Post 54),
Its bronze script is
similar to shell bone script.
Its big seal script is
The fingers of hand are langer, more like a hand.
the bottom one
means Brush (with a hand holding the brush).
The top one
is a radical, which means bamboo related. Becaues all brush body was made from bamboo.
Its clerical script is
same as the small seal script, the top one is a radical meaning something related to bamboo. The bottom one means brush.
Gradually, the bottom one has been replaced by the characters with the radical. The bottom one has not used as Brush any more. It became a modal particle without meaning, and not used nowadays. But it keeps its Brush meaning if it is in a character as a radical.
Its current standard printing script for tranditional character is
same as the clerical script.
Its printing script for simplified character is
on the top is the bamboo related radical, on the bottom is character "Hair". Top is bamboo, and bottom is hair, which is Brush. The hand is disappeared, but it is very understandable.
Its pinyin is "Bi1".