I think that of the palier? In some car brands you hit a dry blow to the omocinetic tip of the palier and leaves, that allows you to put the rubber bellow and with a little push the good buelves to fit and ready.
Peugeot I think it is not so you need a dilator or manual that is a plastic cone and you suffer to push as crazy or pneumatic that is like a spider that with the spatter legs the rubber and you can pass it to its site.
If you are going to use dilator, buy a standard bellows that are more flesible than those of origin.