First of all i create one new UDF called as U_CatNo then i create one User Define Query.
SELECT T0.[U_CatNo] FROM OSCN T0 WHERE T0.[ItemCode] = $[$37.4.0]
and i define that U_CatNo to Bill of Material Window.
also define User Define Value on that field.
i provide you the screenshot also
I wait for your warm replay.