Threaded Bush Insert
These are a bush which features thread on the inner and external faces. They are simple to install typically using standard thread sizes.
They can be used to repair parts with damaged thread or for interfaces between a components of different strength materials. These are typically used on high end aluminium mountain bike crank arms where high strength steel pedals would screw in.
Shouldered Bush Insert
An engineered bush with a shoulder to react loads applied. These are typically pressed in and utilise a mechanism to stop the bush rotating, such as adhesives, knurling or grub screws.