This is to stop small offcuts dropping in the blade gap. Probably the simplest 3d model on thingiverse but the concept is very useful.
The size of this is for my old Burgess bandsaw but obviously other sizes are easily constructed with sketchup etc. (now customizable)

Print out blank. Turn it over, align the blank with the guide and cut the slot with the saw you are fitting it to. Flip it back the correct way and position it. Mark the location of the alignment notch then cut that out. Fit the completed insert.