Some model engines use Japanese Industrial Standard (JIS) head screws. This is a slightly different design than an American Phillips head screw. A normal Phillips screwdriver will not properly engage a JIS screw. It will tend to cam out and round the slot. I need to get a JIS screwdriver myself, but I have not found a source.
You can tell a JIS screw by looking at it. The X slot will look the same as a normal Phillips but it will have a little dot outside of the X.
Last edited by JPMacG; 04-07-2014 at 05:22 PM.