A lot of people still unaware that most mechanical lockers in island-wide still do not accept new Singapore coins. What happen if you insert a new Singapore coin in such machine? Oh the new coin will just get stuck at the coin slot without going down the coin channel and worse your big fingers are not able to pull out the stuck coin.
One easy solution is use a new super strong magnet you can get from unused HDD. See the below picture, new Singapore coin can easily pick out by magnetic.