Since this was recently discussed in a TS thread, I thought I would post a thread on this. Plus I had to put a STI ambi TS on my SA Compact. First, this applies for both single TS and ambi TS. A more positive "snicking" off on a TS will prevent it from accidentally disengage from the "on" position. Here's is an area to modify if your TS doesn't have that positive clicking off. Look at the concave area that the plunger comes into contact with. Also look at the corner that the plunger needs to break for it to click off. The sharper and more square the corner, the harder it is to click off. And the rounder the corner, the easier for it to over come the force of the plunger spring. So if you want a more positive click (ie harder for the TS to disengage). Take a file and increase the concave and sharpen corner. There's no magic measurement on how much to file or how deep to go. It's different for every gun. Just remember that it's easier to take metal off than to add it back on. So go slowly and keep on testing the feel. Once you're done, take some 600-800 grit sandpaper and polish up the area to remove file marks.