Kamasutra 7.2.23

7.2.23

tasminn anekākṛtivikalpāny apadravyāṇi yojayet/

In the hole made in the lingam a man may put Apadravyas of various forms, such as the "round," the "round on one side," the "wooden mortar," the "flower," the "armlet." the "bone of the heron," the "goad of the elephant," the "collection of eight balls," the "lock of hair," the "place where four roads meet," and other things named according to their forms and means of using them. All these Apadravyas should be rough on the outside according to their requirements.