The perfect solution.
I needed something to make a 16-lb. window seat open and close more easily. Friction hinges were unreliable. The calculator at Gasspringsshop.com is an amazing app! I entered the most accurate info I could. It recommended a 6-15-100, which I ordered. But after reading the website more thoroughly, I found I could reduce the force on the hinges with something smaller, a 4-12-150. So I asked Héctor in customer service to cancel the order and let me start again, this time with the smaller spring. He was very polite understanding and wonderful to work with. Couldn't have been easier! The smaller spring works like a charm. Now the window seat opens and closes easily and stays wherever I put it without falling on my head or fingers. I am a big fan of these springs, and I'll be looking for other uses. And I'll get them here, at Gasspringsshop.com.