My McMaster-Carr springs have arrived. The one on the left is the heavy duty alternative and stocker is on the right. The heavy duty version has a thicker wire diameter and more coils. It's quite a bit stiffer. I was concerned it may be too stiff. I installed it and it works great. Before I could bump the lever with one finger and flash the brake light, but now I have too squeeze it to light it. The heavier spring doesn't affect the master cylinder and brake operation either. I need to go on a group ride before I call it a success though. If anyone needs one let me know; I have nine left.