side faces thereof the shafts 19 are on a common axis and may be made of synthetic resin for example and may be formed integrally with the projections 16 as shown in fig4 6 when temporarily fixing the body 12 of the box to the vehicle body 11 the shafts 19 are inserted into the hooks 14 a with the brackets 14 fitted into the guide grooves 18 such that the body 12 is rotatable about the axis of the shafts 19 the width w 1 of the guide groove 18 is set almost equal to the width w 2 of the bracket 14 this is to prevent a gap existing between the guide groove 18 and the bracket 14 when the bracket 14 is fitted into the guide groove 18 stops 21 project from the front ends of the projections 16 referring to fig7 when the body 12 is rotated on the shaft axis in order to open the opening 11 a of the vehicle body 11 the stops 21 contact the vehicle body 11 to limit the amount of rotation of the body 12 reinforcing ribs 22 may be integrally formed between the stops 21 and the projections 16 to prevent the stops 21 from being deformed or.