Thank you, thank you for these durable springs! I've been doing pilates on mats for many years, but I gave up for many years, big mistake! Anyway, I found a Malibu Pilates Pro chair for sale locally and bought a DVD on ebay, there were some moves I couldn't do because the springs weren't firm enough for me, I'm 5ft 10" and 185 pounds. I put her on my chair and finally I can do her like a pike! As my powers grow, these sources will be very useful!