This is an old favorite of mine and thousands of other project builders including scores of HAM Radio builders. This model has the screw on top and can be disassembled if need be.

 The cutting head is heat treated carbon steel and doesn't wear fast with normal use. I had one for 30 years and the spring broke, not the blade! 

The humble nibbling tool is great for cutting about any crazy size hole in plastic, aluminum and light 18 gauge steel. Custom car radio installers use them for enlarging to make things fit. If they don't, they should!

These are made in Taiwan. My experience is I have found Taiwan steel closer to US steel than others.

Luthier folk need to modify the blade to use these for their purposes. Check my other items--all kinds of stuff! Thanks. WP4DMV..73!