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Furthering what Joe has said....

I've seen MANY instances where the fingerbuttons have been replaced and the new buttons lack the step on the underside of the button that virtually extends the stem. If you remove the old fingerbuttons that have a step... put on buttons with no step... and put the old felts/corks back in... your vertical piston alignment will be off big time.

Good idea, but brass will resist corrosion better:
http://www.onlinemetals.com/merchant.cf ... top_cat=79

Shims or inserts are a very respectable way to assist in alignment and elongation. I do it frequently. However, aluminum is not a compatible metal with brass or steel. Unless it is anodized, it will react to oils and sweat which produce oxides that will get into the casings and can damage the valves. Go with brass or nickel-silver. Or just have a shop turn you out a proper length set of stems (its really quite simple). Just my 2¢.

D.C. Oberloh
Oberloh Woodwind and Brass Works
http://www.oberloh.com" target="_blank