Hot answers tagged shimano
Those are M5 button head cap screws (the entire name is needed to specific the exact part), usually 8mm or 10mm long. You can buy them from any fastener supplier, and many hardware shops as well as bike shops.
Given its only a month old - return to the shop for the first "tune-up" which is standard in most parts of the world. If you bought the bike on line, you can either learn to do it yourself or take it a bike shop and pay for a tuneup. Depends on your mechanical aptitude. Sounds like your bike mechanic visit missed something.
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