PURPOSE: To dispense with the insert forming method, simplity the structure and improve the freedom of design by applying threading work to the female hole formed by molding at the resin-made fixing part of an exterior part, and mounting a unique diameter type threaded bolt in the female thread part.

CONSTITUTION: A female hole 10 is formed together with a resin-made fixing part 7 by molding, and then on the inner surface of the hole 10 a female thread 10a is formed by threading work. A unique diameter type threaded bolt 20 has a large and a small diameter threaded male thread partions 20a, 20b. The large diameter thread portion 20a is threadably fitted in the female hole 10 of the fixing part 7 while the small diameter male thread portion 20b is inserted in the mounting hole and the like of the roof part of a vehicle. The threadably contacting area of the part 20a is increased with its large diameter, thereby assuring a large fixing strength.