Tuning Screw size for HW97k

It's the larger of the 2 trigger guard screws likely an M5 or M6 since the smaller rear is an M4. You can check your front stock screw that's an M5 to see if it's the size.

All else fails you can remove the sction from the stock and unscrew the front trigger guard threaded mounting receptacle and match a screw to it at the Hardware store. Careful theres a washer underneath it.

It's a critical mounting point that yours is missing the screw. If you biught it new contact the dealer. If bought used likely he couldn't get the safety to work properly that's why he probably removed it. Surprised if it's as accurate as it should be though.
 
One thing I have always done on my springers is to replace the slotted screws with hex head allen screws. Not only do they look better, they are also a better quality screw. The hex head stops the screw heads from getting bunged up like slotted or phillips head screws become. Metris has become so pipular that most hardware stores now carry them..