Основание I think simply is a lower part of a point, kind of holder.

To view the picture of a tanged point, click on link below.

tanged point
Tanged points are projectile points that have a tang at one end to facilitate hafting. A tang is made by retouching one, or more usually both edges, in order to create a projection that is thinner than the width of the blank. This projection is then fitted into the arrow shaft.

Tanged point - A1 are projectile points that are made from naturally pointed blade blanks that have no, or little, retouch except for the tang which is created by direct retouch.

http://www.hf.uio.no/iakh/forskning/sarc/iakh/lithic/PROJ.ht...