Thumb Piece screw size - Taurus 85UL?

Anyone happen to know the thumb piece screw size (thread size and length) for a Taurus 85ul (.38 special). I have lost the screw and Taurus wants close to $6 to send a new screw. Lewis in customer service @ Taurus says they don't know the size of the screw, and Taurus's lifetime warranty only applies if I ship them the gun for repair.

Pisses me off. I only have put around 100 rounds through it in 2 plus years of owning it. I took it out to take it to the range, and noticed the thumb piece was missing, found that, but not the screw. :mad: