I needed to T into a 12 VDC source wire on my compact tractor. Space on the wire for access was limited. I had never before used a T Tap connector but it looked perfect for this situation. The wire insulation was thick and hard, and looked like the conductor itself might be 10 gauge, though I could not actually see the bare copper wire anywhere. I selected the largest connector from the kit (yellow) and used it. As expected, piercing the insulation was difficult and required the use of a vise-grip pliers and adjusting them in small increments until the cover was firmly latched. The spade terminal made downstream connection very simple. So far, a month later all is working as expected.
Worked exactly the way I hoped for.think of making a stronger version for commercial use. Good product.