What is the 'lifeline ridge"

A life-line ridge is a bump on the left side of the palm area of the grip. This helps with precise placement of the hand as it “pops” into place. 

The main idea is that the ridge is high enough to make its presence noticeable when placing your palm. With only 0.7mm height, you will feel it when it “snaps” in your palm’s lifeline. When on full draw, the lifeline disappears, as it is much thinner than your skin tissue thickness. 

The life-line ridge is available for all plastic, glass and wooden grips.

Some models (like the I AM grips) do not have an option to add a lifeline. This is because the inner edge (left for right handed archers) is sharp enough so it works in the same way for the placement of the palm.