Different geometries to try with M3 Heated Inserts.

Initial testing done with PETG - simple 4mm diameter hole featured the best results for generic M3 heated-inserts.

Necking down towards the bottom of the hole to form a counterbore appeared to increase the difficulty in aligning the insert and also created secondary issues with residual plastic venting towards the part's surface.

Potential extensions: Chamfering the hole's edge may aid in initial alignment of the insert and alleviate issues with venting.