16T/20T GT2 Pulley spacer

Replacement part of Anet 6mm spacer commonly used
or
generic GT2 16T/20T pulley spacer with design optimizations
Warning : Don't push or pull the screw on it ! You have to screw it, to keep the shape of spacer and keep its hardness and rigidity
You should be able to screw it very easily, only a small part is in direct contact