SELECT COUNT(moment_of_inertia_in_torsion__j___cm_4__) FROM table_2071644_1 WHERE web_thickness__mm_ = "4.7"
What is the number for the moment of intertia in torsion (j) (cm 4) for the 4.7 web thickness (mm)?
CREATE TABLE table_2071644_1 (
    moment_of_inertia_in_torsion__j___cm_4__ VARCHAR,
    web_thickness__mm_ VARCHAR
)