A stem with a 25.4 clamp is preferred for 25.4 handlebars. I am using a Nitto Technomic quill stem (26.0 clamp) with my 1988 Fuji Pulsar's original handlebars (25.4). My shim is home-made from an empty solvent can (steel material). No slippage using the shim. Some use aluminum material from an empty pop can, but my choice is steel over aluminum. Whatever you choose, I see no reason to spend around $10 retail for a shim.