Brass Inserts allow the screw/bolt to be repeatedly screwed in/out with little risk of the thread giving up (stripping).
As shown on the Solder Buddy videos – these can be used to create professional enclosures/clam-shell/cases for your products/test rigs. Unless you are snap-fitting or designing for 1-time assembly and intend to use self-tapping screws, these are an ideal alternative.
Although Amazon is pretty competitive on price, I have yet to find anything cheaper than RS for Brass Inserts.
For example, M3 is a good size (if you are Metric).