the seven base units of the SI system of units (meter, kilogram, second, ampere, kelvin, candela, and mole)
We are not the wonders, though we were created by man
Its a man made system.
We are not the dwarfs, for our names are not proper
These units are generally not capitalized.
We are not the days, though they each contain one of our own
Days are made up of seconds, one of the base units.
We are not the sins, for while our own kind exploits us, together we are pure.
These are the base ("pure") units, which are combined to make up the other derivative units in the SI system.
In science, we are the standard.
They are the standard units used in the scientific world (as opposed to Imperial units used colloquially)