Two of my favorite tools are homemade. I find homemade studs with slotted ends for a screwdriver very useful for aligning parts and holding them in position while I get bolts started (e.g., gaskets, headers, bell housing, water pump, etc.). The other is a stubby spark plug socket for working in tight spaces behind headers. I cut it so there are just enough flats inside the socket to grip the plug, and just enough flats on the outside for a box end or open end wrench.
