1classifier for bombs, missiles, satellites etc
2classifier for small objects: coins, badges, rings, carved seals, chess pieces, eggs, fingerprints etc (more formal than 個|个)
3(on product packaging) classifier for flat items (from Japanese 枚 "mai")
4(old) stick used as a gag to prevent soldiers from talking while sneaking up on the enemy
Examples
wǒ我xū yào需要xiān先fàng放yì一méi枚yìng bì硬币ma吗？
我需要先放一枚硬币吗？
Do I need to put a coin in first?
我的背包里有几枚邮票。
I have some stamps in my bag.
他半夜给了我一枚戒指。
He gave me a ring at midnight.