I use these spring in my old Mahillon euphonium, witch are a perfect fit, and a little bit bigger then the original ones, witch makes it a little harder to push down the valve, bud it comes up much faster :) very nice :) they also get less fast "stuck" , so they need less lubricant to keep them going, bud a little more finger muscle. They are flawless bronze, and perfect for the job. Very good springs :)