Compatibility summary
Your Singapore plug may fit in Montserrat outlets, as both use at least one common plug type.
Plug comparison
Singapore plug types: G
Montserrat plug types: A B G
Both countries share at least one plug type (G and A B G), so some plugs may work without an adapter. Check your appliance.
Voltage comparison
Singapore: 230V, 50Hz
Montserrat: 230V, 60Hz
Voltage difference is within a range many devices tolerate; check your appliance label.