I'm not familiar with the ST 9 but with regards to Old No 7's post I generally put the open end of the spring towards the barrel, so 6 oclock if the slide it upside down for assembly or 12 oclock if it's right side up.
No issues with the spring trying to poke out the end of the slide.
In Memory of Paul "Dietrich" Stines.
Dad: Say something nice to your cousin Shirley
Dietrich: For a fat girl you sure don't sweat much.
Cue sound of Head slap.
RIP Muggsy & TMan
"If you are a warrior legally authorized to carry a weapon and you step outside without that weapon, then you become a sheep, pretending that JOCKO will not come today."