The screen Jack is a holding frame so you can keep things connected when you are diagnosing (think like a cars tire jack)
Here is the best tool set for working on iPhones: [product|IF145-198-8|iOpener tool kit]. Some people prefer the [product|IF145-243|iSclack] Vs the single cup tool.
I stand corrected! The IFIXIT tool [product|IF145-383|gTool 360] is what I was thinking of.
gTool is a very different beast! ScreenJack Pro
iFIXIT's listing: [product|IF145-281|gTool Screen Jack] is the original model and the [product|IF145-281-2|gTool Screen Jack universal] (no image) I think is the second generation.