The triax spare system is really quite simple.
First you need to use plastic or a ball that goes very straight.
Find a line through practice that works for you. I find that for me for the left side spares, 7,4,and 2. I need to set my left foot on the 10 board and face the 7 pin with my right shoulder, my target mark being the third arrow.Now using my plastic spare ball release the ball flat with no hook. Be sure you get your set up angle correct. See the ball roll right over the arrow mark.Next for the 4 pin move your left foot over 3 boards to the left, in my case this would be board 13 and again line up to roll the ball over the third arrow. The 2 pin would be to move left foot over to the 16 board and cross the third arrow.
Now for the 10 pin, for me I set my left foot on board 40, face the 10 pin with my right shoulder and use the fourth arrow as my target mark.I also find that keeping the index finger in close helps you roll the ball with no hook.
Then again move 3 boards to your right with your feet to board 37 and roll over the fourth arrow to pick up the 6 pin, use the 34 for the 3 pin.
You will need to practice and find what target and where to place your feet that through trial and error works the best for you. Once you know your set up position, then make minor changes in your target mark to fit the lane conditions for the lane. Key is to use plastic and roll it straight and accurate.
Thanks to Duke for the picture, we should all have this spare thing under controll. Good luck.
Girlscout