Abstract: A stop assembly comprising a generally cylindrical body whose outer surface is adapted for engaging the interior cylindrical surface of a hollow core, a plurality of fingers secured to the body for pivotal movement about axes generally parallel to that of the core between first positions in which the fingers lie radially within the outer surface of the body and second positions in which the fingers project beyond the outer surface for engaging an end surface of the core, each of the fingers having a core engagement surface lying in a plane generally perpendicular to the outer surface of the body and adapted for engaging the core end surface and a generally oppositely-facing camming surface inclined relative to the core engagement surface, the fingers being biased outwardly and no fixed portion of the assembly lying radially outwardly of the outer surface so that the entire assembly may be inserted into and through a core having an interior cylindrical surface of diameter not substantially greater than that of