Open Wound Ends
This isn’t an actual spring type, it is a type of ends, open ends. Open wound ends give you the opportunity to get more elasticity out of your spring as well as a smaller solid height. For example, if you have a spring with 5 active coils (open wound coils) and 7 total coils (due to the close wound coils on the ends) you may take those closed coils out to be left with 5 active total coils. In another case, if your spring is too stiff and you need for this spring to travel more, you may turn one of the close wound end coils into an open wound coil thus giving you an additional active coil. Remember, more active coils make your spring weaker.