One note for everybody: if Dr. Bot is asking about aluminum extrusion T-Nuts, then they need T-Nuts which are compatible with those extrusions. I know for a fact (ie - I got burned professionally on this) that you cannot mix Bosch extrusions and 80/20 T-Nuts (and vice-versa) because the T slots on the extrusions are shaped differently.
However, $3.25 is about the right price for milling machine T-Slot nuts. I was able to find some online for about $2.50, but they were 5/16, not 1/4-20.
